sagemathgh-36999: Rename `install-requires.txt` to `version_requirements.txt`
    
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As discussed in sagemath#36982:
- the name "install-requires"  has become outdated with the transition
to the new names set by the `pyproject.toml` format (see https://setupto
ols.pypa.io/en/latest/userguide/dependency_management.html#declaring-
required-dependency, compare the tabs "pyproject.toml" vs. "setup.cfg")
- this will help with sagemath#35890, as
GitHub will be able to just read the `version_requirements.txt` files

sagemath#36982 (comment)

Notes for reviewers:
- **This is a simple, limited-scope improvement and not intended as a
long-term commitment to the format of the files in build/pkgs/....**
- PRs sagemath#37430, sagemath#37350, sagemath#36740 remove direct access to build/pkgs in favor
of using the sage_bootstrap API (sage --package).

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example "Fixes sagemath#12345". -->
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- [ ] I have updated the documentation accordingly.

### ⌛ Dependencies

<!-- List all open PRs that this PR logically depends on
- sagemath#12345: short description why this is a dependency
- sagemath#34567: ...
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- Depends on sagemath#37401

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URL: sagemath#36999
Reported by: Matthias Köppe
Reviewer(s): Dima Pasechnik, Kwankyu Lee, Nathan Dunfield

sagemathgh-36999: Rename `install-requires.txt` to `version_requirements.txt`
    
<!-- ^^^^^
Please provide a concise, informative and self-explanatory title.
Don't put issue numbers in there, do this in the PR body below.
For example, instead of "Fixes sagemath#1234" use "Introduce new method to
calculate 1+1"
-->
<!-- Describe your changes here in detail -->

As discussed in sagemath#36982:
- the name "install-requires"  has become outdated with the transition
to the new names set by the `pyproject.toml` format (see https://setupto
ols.pypa.io/en/latest/userguide/dependency_management.html#declaring-
required-dependency, compare the tabs "pyproject.toml" vs. "setup.cfg")
- this will help with sagemath#35890, as
GitHub will be able to just read the `version_requirements.txt` files

sagemath#36982 (comment)

Notes for reviewers:
- **This is a simple, limited-scope improvement and not intended as a
long-term commitment to the format of the files in build/pkgs/....**
- PRs sagemath#37430, sagemath#37350, sagemath#36740 remove direct access to build/pkgs in favor
of using the sage_bootstrap API (sage --package).

<!-- Why is this change required? What problem does it solve? -->
<!-- If this PR resolves an open issue, please link to it here. For
example "Fixes sagemath#12345". -->
<!-- If your change requires a documentation PR, please link it
appropriately. -->

### 📝 Checklist

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- [x] The description explains in detail what this PR is about.
- [x] I have linked a relevant issue or discussion.
- [ ] I have created tests covering the changes.
- [ ] I have updated the documentation accordingly.

### ⌛ Dependencies

<!-- List all open PRs that this PR logically depends on
- sagemath#12345: short description why this is a dependency
- sagemath#34567: ...
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- Depends on sagemath#37401

<!-- If you're unsure about any of these, don't hesitate to ask. We're
here to help! -->
    
URL: sagemath#36999
Reported by: Matthias Köppe
Reviewer(s): Dima Pasechnik, Kwankyu Lee, Nathan Dunfield

sagemathgh-37430: Refactor `bootstrap`, `bootstrap-conda`, `m4/sage_spkg_collect.m4`, `sage-spkg-info` through `sage --package properties`, `sage-get-system-packages`
    
<!-- ^^^^^
Please provide a concise, informative and self-explanatory title.
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<!-- Describe your changes here in detail -->

Using the command `sage --package properties` added in
sagemath#37018, we eliminate some direct
references to `build/pkgs/` from various scripts and reduce code
duplication in reading SPKG metadata.

Using other `sage --package` commands, we also simplify the code for
`bootstrap -s` and `bootstrap -D`.

Review instructions: Note that there are changes to the
`bootstrap`-generated file `m4/sage_spkg_configures.m4`:
- The macro `SAGE_SPKG_COLLECT_INIT` is now called explicitly, with an
argument (the full list of packages).
- Lines such as `m4_define([SPKG_INSTALL_REQUIRES_exceptiongroup],
[['exceptiongroup; python_version<\"3.11\"',]])dnl` are added for use by
the macro `SAGE_PYTHON_PACKAGE_CHECK` (replacing direct access to
`version_requirements.txt` files)

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example "Fixes sagemath#12345". -->
This is:
- Split out from sagemath#36740
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- [x] I have linked a relevant issue or discussion.
- [ ] I have created tests covering the changes.
- [ ] I have updated the documentation accordingly.

### ⌛ Dependencies

<!-- List all open PRs that this PR logically depends on
- sagemath#12345: short description why this is a dependency
- sagemath#34567: ...
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URL: sagemath#37430
Reported by: Matthias Köppe
Reviewer(s): Julian Rüth, Kwankyu Lee, Matthias Köppe, Tobias Diez