This should mitigate some of the regressions introduced in
https://chromium-review.googlesource.com/c/v8/v8/+/2972910.
Changes:
- Use a single Zone for all init. expressions in InstanceBuilder.
- Specialize DecodeFunctionBody() for init. expressions.

Bug: v8:11895, chromium:1226551
Change-Id: Ie39f981efeaa89e57f8ccb68903c6e7cc1cb7f09
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3009465
Commit-Queue: Manos Koukoutos <manoskouk@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75597}