[top-level-await] Sync implementation with spec text

[test262-pr-bot]

The module evaluation machinery has undergone non-trivial refactoring since implementation. Sync up the comments and code for maintenance.

Notably,

• Actually use the kEvaluatingAsync status (previously conflated under kEvaluated)
• [[IsAsyncEvaluating]] -> [[IsAsyncEvaluation]]
• GatherAsyncParentCompletions -> GatherAvailableAncestors
• async -> has_toplevel_await
• kAsyncModule -> kModuleWithTopLevelAwait

Bug: 347060515 Change-Id: Ia2c35d5b42ee9f58db841cdfcaef9d17b018c9c6 Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/5636701 Reviewed-by: Adam Klein \adamk@chromium.org Commit-Queue: Shu-yu Guo \syg@chromium.org Cr-Commit-Position: refs/heads/main@{#94591}