RFR: 8266973: Migrate to ClassHierarchyIterator when enumerating subclasses [v3]

[Vladimir Ivanov]

> Replace ad-hoc recursion when enumerating subclasses with `ClassHierarchyIterator`.
> 
> Found 3 occurrences:
> - `Dependencies::find_finalizable_subclass()`
> - `reinitialize_vtable_of()`
> - `VM_RedefineClasses::increment_class_counter()`
> 
> Testing:
> - [x] hs-tier1 - hs-tier4

Vladimir Ivanov has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains three commits:

 - Merge branch 'master' into 8266973.iterator
 - JFR
 - 8266973: Migrate to ClassHierarchyIterator when enumerating subclasses

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Changes: https://git.openjdk.java.net/jdk/pull/3995/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3995&range=02
  Stats: 101 lines in 9 files changed: 8 ins; 54 del; 39 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3995.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3995/head:pull/3995

PR: https://git.openjdk.java.net/jdk/pull/3995