RFR: 8329628: Additional changes after JDK-8329332

[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

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Commit messages:
 - Removed commented code. Fix indent.
 - 8329628: Additional changes after JDK-8329332

Changes: https://git.openjdk.org/jdk/pull/18665/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18665&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8329628
  Stats: 103 lines in 34 files changed: 15 ins; 21 del; 67 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