openjdk-21 (security release) - bundle gtest, refresh problemlist

This MP achieves the following: bundle gtest library to allow native tests in the backports (failing to compile in Jammy and focal due to the old version) and refreshes problem lists for the release.

Changes:

 * OpenJDK 21.0.1 release, build 12.
    - CVE-2023-22081, CVE-2023-22025.
    - Release notes:
      https://www.oracle.com/java/technologies/javase/21-0-1-relnotes.html

  * d/watch: use release version format.
  * d/copyright: include google test license.
  * d/rules, d/watch: bundle google test library.
  * d/patches: remove build_gtest.patch.
  * d/tests: refresh problem lists.
  * d/p/exclude_broken_tests.patch: drop patch.

Testing:

• rebuild in PPA: https://launchpad.net/~vpa1977/+archive/ubuntu/october-21/+sourcepub/15218410/+listing-archive-extra
• rebuild in sid chroot - all tests pass.

Note: copyright generator needs to be fixed, as it generates copyright file with multiple lintian errors