[Clang][Sema] Tweak tryCaptureVariable for unevaluated lambdas (#93206)

This patch picks up #78598 with the hope that we can address such
crashes in `tryCaptureVariable()` for unevaluated lambdas.

In addition to `tryCaptureVariable()`, this also contains several other
fixes on e.g. lambda parsing/dependencies.

Fixes #63845
Fixes #67260
Fixes #69307
Fixes #88081
Fixes #89496
Fixes #90669
Fixes #91633