In very rare cases we open CodeSpaceWriteScopes for multiple native
modules at the same time, e.g. for tier down (debugging) via

  ExecuteCompilationUnits
--> PublishCompilationResults
--> OnFinishedUnits
--> TriggerCallbacks
--> AsyncCompileJob::CompilationStateCallback::call
--> WasmEngine::UpdateNativeModuleCache
--> RecompileNativeModule [for tier down]
--> InitializeRecompilation
--> FindFunctionsToRecompile
--> CodeSpaceWriteScope

Fixing this would be difficult because we actually want to keep the
CodeSpaceWriteScope open during subsequent publishing. So instead,
remove the assumption that scopes are always only open for one module at
a time.
In order to do this, we remove the {code_space_write_nesting_level_}
counter and instead use the {current_native_module_} field in all
configurations to check whether a scope is currently open, and for which
module.

R=jkummerow@chromium.org

Bug: v8:12644, v8:11974
Change-Id: Idd24c87f5938c43e867c41fa1cd3879def6f3873
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3484317Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79286}