The interpreter is not an execution tier in production any more. It's
only used in tests.
Thus, remove {ExecutionTier::kInterpreter} and instead add a
{TestExecutionTier} that still has {kInterpreter}.

If needed (in {TestingModuleBuilder::execution_tier()}), we translate
back from {TestExecutionTier} to {ExecutionTier} (for {kLiftoff} and
{kTurboFan} only).

The {TraceMemoryOperation} method, which is shared between interpreter
and production code, now receives a {base::Optional<ExecutionTier>}, and
we will just pass en empty optional if called from the interpreter.

R=thibaudm@chromium.org

Bug: v8:10389
Change-Id: Ibe133b91e8dca6d6edbfaee5ffa0d7fe72ed6d64
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2335186Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69260}