A Wasm module's start function might be imported from JavaScript, and
as such might contain calls to Blink. For such a case, we must make
sure that an "incumbent context" is available.
See microtask queue handling for a similar example.

Bug: chromium:1096558
Change-Id: I2e3c0fc20d4e3581e490822c3ac63ce2c5e1e990
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2284982Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68760}