This changes the WasmGraphBuilder to use the GraphAssembler for storing
the current effect and control, instead of having separate fields.
This will allow us to use GraphAssembler methods anywhere in the
WasmGraphBuilder without first transferring the WasmGraphBuilder's
effect and control to the GraphAssembler and storing it back afterwards.

Some methods (StackCheck, BuildCallToRuntimeWithContext) have been
changed to work on the current effect and control instead of receiving
them as parameters. This is necessary to also use the GraphAssembler
there, and it makes the code a bit easier.

R=ecmziegler@chromium.org

Bug: v8:10123
Change-Id: Ia9f6359cfe44a67a875c3eb0fe51f87db8bd17db
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2017470
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65975}