RFR: 8336468: Reflection and MethodHandles should use more precise initializer checks

[Aleksey Shipilev]

This PR should cover the Reflection/MethodHandles part of [JDK-8336103](https://bugs.openjdk.org/browse/JDK-8336103).
 
There are places where we change the behavior: `clinit` would now be recorded as "method", instead of "constructor". Tracing back the uses of `get_flags`: it is used for initializing `java.lang.ClassFrameInfo.flags`. There seem to be no readers for this field in VM. Java side for `j.l.CFI` does not seem to check any method/constructor flags. So I would say this change in behavior is not really visible, and there is no need to try and keep the old (odd) behavior.

I also inlined the `select_method` definition, which allows for a bit more straight-forward local code, and obviates the need for wrapping things with `methodHandle`.

@mlchung, you probably want to look at this more closely.

Additional testing:
 - [x] Linux x86_64 server fastdebug, `tier1`
 - [ ] Linux x86_64 server fastdebug, `all`

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Commit messages:
 - Remove unnecessary handle-izing
 - Fix
 - Fix

Changes: https://git.openjdk.org/jdk/pull/20192/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20192&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8336468
  Stats: 38 lines in 5 files changed: 14 ins; 10 del; 14 mod
  Patch: https://git.openjdk.org/jdk/pull/20192.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20192/head:pull/20192

PR: https://git.openjdk.org/jdk/pull/20192