8365880: Shenandoah: Unify memory usage accounting in ShenandoahFreeSet

[kdnilsen]

This PR eliminates redundant bookkeeping that had been carried out by both ShenandoahGeneration and ShenandoahFreeSet. In the new code, we keep a single tally of relevant information within ShenandoahFreeSet.
Queries serviced by ShenandoahGeneration are now delegated to ShenandoahFreeSet.

This change eliminates rare and troublesome assertion failures that were often raised when the ShenandoahFreeSet tallies did not match the ShenandoahGeneration tallies. These assertion failures resulted because the two sets of books are updated at different times, using different synchronization mechanisms.

The other benefit of this change is that we have less synchronization overhead because we only have to maintain a single set of books.

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Progress

• Change must be properly reviewed (1 review required, with at least 1 Reviewer)
• Change must not contain extraneous whitespace
• Commit message must refer to an issue

Issue

• JDK-8365880: Shenandoah: Unify memory usage accounting in ShenandoahFreeSet (Task - P4)

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk.git pull/26867/head:pull/26867
$ git checkout pull/26867

Update a local copy of the PR:
$ git checkout pull/26867
$ git pull https://git.openjdk.org/jdk.git pull/26867/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 26867

View PR using the GUI difftool:
$ git pr show -t 26867

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/jdk/pull/26867.diff

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[openjdk]

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• hotspot-gc
• shenandoah

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