RFR: 8329628: Additional changes after JDK-8329332 [v2]

[Vladimir Kozlov]

> Additional clean up based on comments (mostly Stefan's) during reviews for [JDK-8329332: Remove CompiledMethod and CodeBlobLayout classes](https://bugs.openjdk.org/browse/JDK-8329332).
> - Renamed `CompiledMethod_lock` to `NMethod_lock`.  (I decided to not change JVMTI's `CompiledMethod[Load|Unload]` names).
> - Renamed `NMethodIterator::all_blobs` to `NMethodIterator::all`.
> - Moved `get_deopt_original_pc()` method from `nmethod` to `frame` class.
> - Reverted `CodeCache::find_nmethod()` to previous functionality to allow return `nullptr` and be consistent with `find_blob()`.
> - Cleanup some `(nmethod*)` casts.
> - Use `for (CodeHeap* heap : *_nmethod_heaps) ` in `CodeCache::nmethod_count()` (it was @stefank suggestion,  I don't know how this C++ magic works). I verified it running with `-XX:+PrintNMethodStatistics`.
> 
> Testing tier1-3,xcomp,stress

Vladimir Kozlov has updated the pull request incrementally with one additional commit since the last revision:

  Addresse comments

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Changes:
  - all: https://git.openjdk.org/jdk/pull/18665/files
  - new: https://git.openjdk.org/jdk/pull/18665/files/5a41bd5b..c33c9a6c

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=18665&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=18665&range=00-01

  Stats: 57 lines in 18 files changed: 8 ins; 0 del; 49 mod
  Patch: https://git.openjdk.org/jdk/pull/18665.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18665/head:pull/18665

PR: https://git.openjdk.org/jdk/pull/18665