Integrated: Restrict generational mode to adaptive heuristic

[William Kemper]

On Fri, 24 Mar 2023 18:59:50 GMT, William Kemper <wkemper at openjdk.org> wrote:

> This is a small change to Shenandoah, but it prevents us from running the tests with the generational mode enabled via a jtreg vm option. This requires us to properly integrate the generational mode with the jtreg tests. There are many test files changed, but the `generational` mode is now handled in the same fashion as other modes (`iu`, `passive`). There are two additional advantages to these changes:
> * We no longer need to run the test suite twice (once in the default mode and again with `-XX:ShenandoahGCMode=generational`).
> * Expanded test coverage, as some tests would spawn their own VMs with permutations of mode and heuristic options that ignored the generational mode.

This pull request has now been integrated.

Changeset: 2785875d
Author:    William Kemper <wkemper at openjdk.org>
URL:       https://git.openjdk.org/shenandoah/commit/2785875de3bf86ab20779c5a24ec7e0f69e452aa
Stats:     1503 lines in 63 files changed: 1153 ins; 309 del; 41 mod

Restrict generational mode to adaptive heuristic

Reviewed-by: shade

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PR: https://git.openjdk.org/shenandoah/pull/233