internal/gen has never been updated for Go 1.17's //go:build tags.
Do that, and add the entry for Unicode 15.0.0.

Unicode 15.0.0 will change 9fff to be a CJK ideograph, which will
break the unicode/runenames example test.
Delete that part of the example.

For golang/go#55079.

Change-Id: I12b0c6d031d6d6e1970c8fe6eb5453fa64c9f365
Reviewed-on: https://go-review.googlesource.com/c/text/+/503035
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>
Auto-Submit: Russ Cox <rsc@golang.org>

go generate ./...

This CL only contains the changes made by go generate ./...

For golang/go#55079.

Change-Id: I840205f9046e6ccaab370b1dc5393aaf02d5fcb2
Reviewed-on: https://go-review.googlesource.com/c/text/+/503036
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>
Auto-Submit: Russ Cox <rsc@golang.org>

Some of the generated sub-test names end up being excessively long,
which doesn't mix well with them being stored as test IDs that track
test runs over time. Replacing test case names with numbers harms
their readability, so start by trimming a few that end up being 500+
bytes in length.

Change-Id: Id3b22105efc08eb1bb51436aa257682d357d662c
Reviewed-on: https://go-review.googlesource.com/c/text/+/506416
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Heschi Kreinick <heschi@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>