RFR: 8303467: Serial: Refactor reference processor

[Thomas Schatzl]

On Wed, 1 Mar 2023 16:43:26 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

> Simple refactoring and removing some unnecessary afterwards.
> 
> Test: tier1-5

Changes requested by tschatzl (Reviewer).

src/hotspot/share/gc/serial/markSweep.cpp line 246:

> 244:   MarkSweep::_string_dedup_requests = new StringDedup::Requests();
> 245: 
> 246:   static AlwaysTrueClosure always_true;

Please put this static into the class as static class member; it's very hard to track if statics are put into random places.
Why we can use `AlwaysTrueClosure` here should probably be documented.
The reference processor for `MarkSweep` can also be a static, as well as `MarkAndPushClosure` initialized statically with that reference processor.

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PR: https://git.openjdk.org/jdk/pull/12809