analyze object when selecting from package

[EnzeXing]

This PR is an updated version of #20424, which fixes a bug in the global initialization checker such that when accessing global object through full path, the checker immediately analyzes the initialization code of the corresponding object.

[test_scala2_library_tasty]

[EnzeXing]

@liufengyun @olhotak test_scala2_library_tasty shows the extra warnings that we have seen have when analyzing with scala2 library tasty. The initialization cycle object Predef -> package object scala -> object IndexedSeq -> object Vector -> object Predef should be already fixed when using the latest version of scala2-library-tasty. Cyclic initialization: object Predef -> object Manifest -> object ManifestFactory -> object Predef should be fixed after we merge #21523. I think it's safe to merge this PR, and possibly conclude issue #18882.

[liufengyun]

@EnzeXing Thank you. I just approved the other PR.

In order to avoid breaking the nightly build, we can add some of the tests to a blacklist if they cannot be reasonably adapted:

• https://github.com/lampepfl/dotty/blob/main/compiler/test/dotc/pos-init-global-scala2-library-tasty.blacklist
• https://github.com/lampepfl/dotty/blob/main/compiler/test/dotc/neg-init-global-scala2-library-tasty.blacklist

This way, we will be sure that the test test_scala2_library_tasty will be green.

[EnzeXing]

I have updated the blacklist and now the tests passed.

[olhotak]

LGTM