Code event handler relies on having WasmEngine having an isolate, which
happens during Snapshot::Initialize.

Note that this fixes a crash (that the WasmEngine doesn't have an
isolate), but does not get gdbjit integration with Wasm working yet (see
https://crbug.com/v8/11908).

Bug: v8:11967,v8:11930
Change-Id: I56c753d3b66d58e49020688bd387a7c040feb0af
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3018054Reviewed-by: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75686}