Using the default cctest TEST(...) macro causes later writes to
FLAG_stack_size to have no effect, because the StackGuard reads
that flag's value during Isolate initialization, which is done
before the test body is executed. This patch changes the two
existing tests that accidentally did this to UNINITIALIZED_TEST,
putting them in charge of Isolate creation, thereby ensuring that
the intended stack size is configured correctly.

Change-Id: Ib030795ef46f23d576f6dbbd26b347ac804b5085
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2862778Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Yang Guo <yangguo@chromium.org>
Auto-Submit: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74309}