Integrated: Restore ShenandoahVerify functionality for generational mode

[earthling-amzn]

On Thu, 18 Mar 2021 15:36:58 GMT, earthling-amzn <github.com+71722661+earthling-amzn at openjdk.org> wrote:

> ### Summary
> 1. Add remembered set to verifier roots for young generation collections
> 2. Don't follow pointers outside the generation during verify traversals
> 3. Verify generation's `used` value
> 4. Correct errors in computing a generation's `used` values
> 
> ### Testing
> 1. Dacapo suite completes without verification errors
> 2. hotspot_gc_shenandoah completes without verification errors

This pull request has now been integrated.

Changeset: bcde2f61
Author:    William Kemper <kemperw at amazon.com>
Committer: Roman Kennke <rkennke at openjdk.org>
URL:       https://git.openjdk.java.net/shenandoah/commit/bcde2f61
Stats:     185 lines in 16 files changed: 154 ins; 6 del; 25 mod

Restore ShenandoahVerify functionality for generational mode

Reviewed-by: rkennke

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PR: https://git.openjdk.java.net/shenandoah/pull/24