This is a pure refactoring to make the {GraphAssembler} available in all
of {WasmGraphBuilder}, including {WasmWrapperGraphBuilder}.
Future CLs will use more features of the {GraphAssembler} for building
wasm graphs.

The {WasmGraphAssembler} class will be extended to contain functionality
only needed (or making sense) in the context of wasm.

Drive-by: Move fields to the end of the {WasmGraphBuilder} class.

R=jkummerow@chromium.org

Bug: v8:10123
Change-Id: Idf44915944882adec75ef002ec577f63b2317a17
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2011825Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65902}