This CL fixes two lock-order-inversion warning in the DefaultPlatform.
The problem was that during shutdown locks get taken in the oposite
order than during initialization.

The first two conflicting locks were the WasmEngine lock and the
lock of the DefaultTaskRunner. During WasmEngine initialization, when
the WasmEngine lock is hold, a foreground task is scheduled, which
requires the TaskRunner lock. During shutdown, the task queue of the
TaskRunner gets drained while holding the TaskRunner lock. Thereby
the destructors of the tasks get executed, and the LogCode task of
the WasmEngine thereby acquires the WasmEngine lock.

The second conflict happens between the WasmEngine lock and the
DefaultPlatform lock, where the DefaultPlatform lock is taken during
WasmEngine initialization when the ForegroundTaskrunner is acquired.
During Shutdown, the DefaultPlatform lock was hold while the task
queue was drained, as described above.

Bug: chromium:1346250
Change-Id: Ib67d0c6cad1372e7c592f40bbe68b0ae31b2976b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3782796
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81911}