RFR: 8338695: GenShen: Clean up jtreg tests

[Y. Srinivas Ramakrishna]

On Wed, 21 Aug 2024 17:47:48 GMT, William Kemper <wkemper at openjdk.org> wrote:

> * Reformat new jtreg tests for generational mode
> * Run tests with verifier enabled first
> * Include generational mode in barrier enable/disable tests (and fix passive mode)
> 
> ## Testing
> 
> * GHA
> * internal tests
> * make exploded-test TEST="hotspot_gc_shenandoah"

LGTM.

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Marked as reviewed by ysr (Committer).

PR Review: https://git.openjdk.org/shenandoah/pull/480#pullrequestreview-2252162589