RFR: 8336466: C2: Parser incorrectly/unnecessarily checks for clinits [v2]

[Aleksey Shipilev]

> As shown in [JDK-8336103](https://bugs.openjdk.org/browse/JDK-8336103), C2 Parser code uses `is_initializer` in the code where we expect to only check for constructors. The fix nominally changes the behavior for C2. I do not believe this is something readily observable, but need to be more explicit.
> 
> Additional testing:
>  - [x]  Linux AArch64 server fastdebug, all (includes Fuzzer and CTW tests), passed as part of JDK-8336103 testing

Aleksey Shipilev has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:

 - Merge branch 'master' into JDK-8336466-c2-parser-init-check
 - Missed the spot
 - Fix

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/20191/files
  - new: https://git.openjdk.org/jdk/pull/20191/files/515aad33..c9fe29b7

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=20191&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=20191&range=00-01

  Stats: 4 lines in 2 files changed: 2 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/20191.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20191/head:pull/20191

PR: https://git.openjdk.org/jdk/pull/20191