RFR: 8338336: GenShen: Cleanup stale TODOs

[Y. Srinivas Ramakrishna]

On Wed, 14 Aug 2024 18:30:14 GMT, William Kemper <wkemper at openjdk.org> wrote:

> First batch of stale TODO cleanup. Code changes here are to complete `TODOs` to hoist affiliation check out of closures in full gc and to use `heap locked or safepoint` assert everywhere (which does not require executing thread to be the VMThread).

Marked as reviewed by ysr (Committer).

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PR Review: https://git.openjdk.org/shenandoah/pull/469#pullrequestreview-2239362634