RFR: 8316229: Enhance class initialization logging [v2]

[David Holmes]

> This change adds some additional debug logging to the class linking and initialization process. It was useful in diagnosing the deadlock described by:
> 
> https://bugs.openjdk.org/browse/JDK-8316469
> 
> See the example output in JBS issue.
> 
> The changes are mostly uncontroversial but I needed to expose a way to access the init thread's name, which can't use the regular `name()` method as the safety check doesn't recognise the calling context as being safe.
> 
> Testing:
>  - manual examination of logging output
>  - ran the only test that enables class+init logging: runtime/logging/ClassInitializationTest.java (no change as expected)
>  - tiers1-3 sanity
> 
> Thanks.

David Holmes has updated the pull request incrementally with two additional commits since the last revision:

 - Extra space
 - Put thread name in quotes.

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/15809/files
  - new: https://git.openjdk.org/jdk/pull/15809/files/8db375eb..d7530af0

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=15809&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=15809&range=00-01

  Stats: 11 lines in 2 files changed: 0 ins; 0 del; 11 mod
  Patch: https://git.openjdk.org/jdk/pull/15809.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15809/head:pull/15809

PR: https://git.openjdk.org/jdk/pull/15809