If a module is not fully (baseline) compiled yet, we cannot reliably
tier it down, because we might not have the wire bytes for all functions
available (in streaming compilation). After baseline compilation
finished, we already check if we need to tier down, and do it then.
Hence we can just skip any tier-down of unfinished modules.

We cannot easily test this in V8 stand-alone, as inspector-test can only
execute one command at a time, so we cannot trigger asynchronous
compilation and then enable the debugger while this is running.

R=thibaudm@chromium.org

Change-Id: I250162a8d3c20599cacebff2f4f540ff6f8b1946
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2953298Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75117}