RFR: 8266973: Migrate to ClassHierarchyIterator when enumerating subclasses

[Coleen Phillimore]

On Wed, 12 May 2021 13:30:09 GMT, Vladimir Ivanov <vlivanov at openjdk.org> wrote:

> 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

This looks really good.  I wonder if you can now make subklass() and next_sibling() functions private to Klass with it having ClassHierarchyIterator as a friend.  If not, I still approve.

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Marked as reviewed by coleenp (Reviewer).

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