Since wrappers do not get optimized,
https://chromium-review.googlesource.com/c/v8/v8/+/2739976 introduced
some performance regression by not caching nodes in the
WasmGraphBuilder. Therefore, we reintroduce caching of the instance
node. We do it in Start() to ensure the effect chain is correct.
Additional changes:
- Change signature of Start() to void.
- Initialize effect and control in Start().
- Rename BuildLoadInstance() -> GetInstance().

Bug: chromium:1189100
Change-Id: I9147f738e67b4f4b822c845e7d33d9fd4ceb65fa
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2804679
Commit-Queue: Manos Koukoutos <manoskouk@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#73824}