RFR: 8329629: GC interfaces should work directly against nmethod instead of CodeBlob [v2]

[Stefan Karlsson]

> The GCs scan and handles nmethods and ignores CodeBlobs of other kinds. The I propose that we stop sending in CodeBlobs to the GCs and make sure to only give them nmethods.
> 
> I removed `void CodeCache::blobs_do(CodeBlobClosure* f)` since there's no more usage of that function. Is this OK?
> 
> I also opted to skipped calling the GC verification code from the iterator code:
> 
> Universe::heap()->verify_nmethod((nmethod*)cb);
> 
> IMHO, I think it is up to the GCs to decide if they want to perform extra nmethod verification. If someone wants to keep this verification in their favorite GC I can add calls to this function where we used to call CodeCache::blobs_do.
> 
> I've only done limited testing and will run extensive testing concurrent with the review.

Stefan Karlsson 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 two additional commits since the last revision:

 - Merge remote-tracking branch 'upstream/master' into 8329629_do_code_blob
 - 8329629: GC interfaces should work directly against nmethod instead of CodeBlob

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/18653/files
  - new: https://git.openjdk.org/jdk/pull/18653/files/e10683e2..1c2bdaea

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=18653&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=18653&range=00-01

  Stats: 5545 lines in 115 files changed: 3743 ins; 1387 del; 415 mod
  Patch: https://git.openjdk.org/jdk/pull/18653.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18653/head:pull/18653

PR: https://git.openjdk.org/jdk/pull/18653