…s variants exist (flutter/flutter#128143)

…s variants exist (flutter/flutter#128143)

…s variants exist (flutter/flutter#128143)

…ts exist (flutter#128143)

Fixes flutter#127090.

flutter#122505 did a few things to speed up the first asset load that a flutter app performs. One of those things was to not include the main asset in its own list of variants in the asset manifest. The idea was that we know that the main asset always exists, so including it in its list of variants is a waste of storage space and loading time (even if the cost was tiny).

However, the assumption that the main asset always exists is wrong. From [Declaring resolution-aware image assets](https://docs.flutter.dev/ui/assets-and-images#resolution-aware), which predates flutter#122505:

> Each entry in the asset section of the pubspec.yaml should correspond to a real file, with the exception of the main asset entry. If the main asset entry doesn�t correspond to a real file, then the asset with the lowest resolution is used as the fallback for devices with device pixel ratios below that resolution. The entry should still be included in the pubspec.yaml manifest, however.

For example, it's valid to declare `assets/image.png` as an asset even if only `assets/3x/image.png` exists on disk.

This fix restores older behavior of including a main asset as a variant of itself in the manifest if it exists.

This fix also includes a non-user-visible behavior change:
* `"dpr"` is no longer a required field in the asset manifest's underlying structure. For the main asset entry, we do not include `"dpr"`. It makes less sense for the tool to decide what the default target dpr for an image should be. This should be left to the framework.

Roll Flutter from 0b74153 to 8a5c22e (46 revisions)

flutter/flutter@0b74153...8a5c22e

2023-06-07 5236035+fzyzcjy@users.noreply.github.com Super tiny MediaQuery doc update (flutter/flutter#127904)
2023-06-07 jacksongardner@google.com Revert "Make inspector weakly referencing the inspected objects." (flutter/flutter#128436)
2023-06-07 leigha.jarett@gmail.com Update menu API docs to help developers migrate to m3 (flutter/flutter#128351)
2023-06-07 andrewrkolos@gmail.com [tools] allow explicitly specifying the JDK to use via a new config setting (flutter/flutter#128264)
2023-06-07 engine-flutter-autoroll@skia.org Roll Flutter Engine from 6f9df0f988c1 to 59d5444cf06c (3 revisions) (flutter/flutter#128376)
2023-06-07 andrewrkolos@gmail.com Do not try to load main/default asset image if only higher-res variants exist (flutter/flutter#128143)
2023-06-07 92602467+99spark@users.noreply.github.com Addressed Ambiguity in transform.scale constructor docs (flutter/flutter#128182)
2023-06-07 5236035+fzyzcjy@users.noreply.github.com Super tiny fix of dead link (flutter/flutter#128160)
2023-06-07 goderbauer@google.com Refactor tests (flutter/flutter#128371)
2023-06-07 polinach@google.com Make inspector weakly referencing the inspected objects. (flutter/flutter#128095)
2023-06-07 goderbauer@google.com Add viewId to PointerEvents (flutter/flutter#128287)
2023-06-07 5236035+fzyzcjy@users.noreply.github.com Show error message in release mode when box is not laid out without losing performance (flutter/flutter#126302)
2023-06-06 engine-flutter-autoroll@skia.org Roll Flutter Engine from ca499463ec2e to 6f9df0f988c1 (1 revision) (flutter/flutter#128363)
2023-06-06 khanhnwin@gmail.com Update Draggable YouTube video link (flutter/flutter#128078)
2023-06-06 31859944+LongCatIsLooong@users.noreply.github.com Remove more rounding hacks from TextPainter (flutter/flutter#127826)
2023-06-06 engine-flutter-autoroll@skia.org Roll Flutter Engine from 4571695f9e76 to ca499463ec2e (1 revision) (flutter/flutter#128356)
2023-06-06 43054281+camsim99@users.noreply.github.com [Android] Update plugin and module templates to use Flutter constant for `compileSdkVersion` (flutter/flutter#128073)
2023-06-06 rmolivares@renzo-olivares.dev handleSelectWord in MultiSelectableSelectionContainerDelegate should handle rects inside of rects (flutter/flutter#127478)
2023-06-06 christopherfujino@gmail.com [flutter_tools] never tree shake 0x20 (space) font codepoints on web (flutter/flutter#128302)
2023-06-06 31859944+LongCatIsLooong@users.noreply.github.com Remove `textScaleFactor` dependent logic from `AppBar` (flutter/flutter#128112)
2023-06-06 engine-flutter-autoroll@skia.org Roll Flutter Engine from b6d37f8f74ad to 4571695f9e76 (6 revisions) (flutter/flutter#128350)
2023-06-06 5236035+fzyzcjy@users.noreply.github.com Fix `Null check operator used on a null value` on TextField with contextMenuBuilder (flutter/flutter#128114)
2023-06-06 engine-flutter-autoroll@skia.org Roll Packages from db4e5c2 to da72219 (10 revisions) (flutter/flutter#128348)
2023-06-06 91688203+yusuf-goog@users.noreply.github.com Updating cirrus docker image to ubuntu focal. (flutter/flutter#128291)
2023-06-06 leigha.jarett@gmail.com Adding example for migrating to navigation drawer (flutter/flutter#128295)
2023-06-06 engine-flutter-autoroll@skia.org Roll Flutter Engine from 722aad83e5fe to b6d37f8f74ad (2 revisions) (flutter/flutter#128341)
2023-06-06 goderbauer@google.com Clean-up viewId casts in flutter_test (flutter/flutter#128256)
2023-06-06 kevinjchisholm@google.com Update cherry-pick issue template to more uniform labels. (flutter/flutter#128333)
2023-06-06 hans.muller@gmail.com Use Material3 in the 2D viewport tests (flutter/flutter#128155)
2023-06-06 nbosch@google.com Use a `show` over a `hide` for `test_api` exports (flutter/flutter#128298)
2023-06-06 engine-flutter-autoroll@skia.org Roll Flutter Engine from aaa7574375a6 to 722aad83e5fe (1 revision) (flutter/flutter#128307)
2023-06-06 leigha.jarett@gmail.com Migration guide for moving from BottomNavigationBar to NavigationBar (flutter/flutter#128263)
2023-06-06 mdebbar@google.com [web] Use 'Uri' instead of 'dart:html' to extract pathname (flutter/flutter#127983)
2023-06-06 engine-flutter-autoroll@skia.org Roll Flutter Engine from 2b353ae90731 to aaa7574375a6 (4 revisions) (flutter/flutter#128301)
2023-06-05 engine-flutter-autoroll@skia.org Roll Flutter Engine from 220ece4d9faa to 2b353ae90731 (1 revision) (flutter/flutter#128293)
2023-06-05 49699333+dependabot[bot]@users.noreply.github.com Bump actions/labeler from 4.0.4 to 4.1.0 (flutter/flutter#128290)
2023-06-05 engine-flutter-autoroll@skia.org Roll Flutter Engine from 7f12e3497428 to 220ece4d9faa (6 revisions) (flutter/flutter#128282)
2023-06-05 jonahwilliams@google.com [framework] attempt non-key solution (flutter/flutter#128273)
2023-06-05 chillers@google.com [labeler] Fix adding labels when name is directory (flutter/flutter#128243)
2023-06-05 katelovett@google.com Remove scrollbar deprecations isAlwaysShown and hoverThickness (flutter/flutter#127351)
2023-06-05 katelovett@google.com Fix update drag error that made NestedScrollView un-scrollable (flutter/flutter#127718)
2023-06-05 engine-flutter-autoroll@skia.org Roll Flutter Engine from f9f72388a4da to 7f12e3497428 (4 revisions) (flutter/flutter#128271)
2023-06-05 goderbauer@google.com Migrate SemanticsBinding to onSemanticsActionEvent (flutter/flutter#128254)
2023-06-05 engine-flutter-autoroll@skia.org Roll Flutter Engine from c838a1b05924 to f9f72388a4da (19 revisions) (flutter/flutter#128252)
2023-06-05 jonahwilliams@google.com [framework] force flexible space background to rebuild. (flutter/flutter#128138)
2023-06-05 engine-flutter-autoroll@skia.org Roll Packages from 75085ed to db4e5c2 (4 revisions) (flutter/flutter#128246)
...

…ariants exist (#128449)

Cherry-picks #128143 onto stable

…s variants exist (flutter/flutter#128143)

…s variants exist (flutter/flutter#128143)

…s variants exist (flutter/flutter#128143)

…s variants exist (flutter/flutter#128143)