WasmGraphBuilder often failed to use GraphAssembler infrastructure and
went with directly invoking graph()->NewNode(). This made the code more
verbose, especially in cases where effect() and control() had to be
passes directly to NewNode().
This CL eliminates these invocations in obvious cases. It does not try
to refactor complicated code with branches, diamond patterns, etc.

Additional changes:
- Define a few more operators in GraphAssembler.
- Move Branch() helper in WasmGraphAssembler.
- Define NumberConstant() helper in WasmGraphAssembler.
- Define Merge() helper with varargs in WasmGraphBuilder.
- Omit IntPtrConstant() wrapper for constant offsets of Load and Store.

Change-Id: I571d5286be8881504cb2060195fbd181d1fce67d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2712804Reviewed-by: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Manos Koukoutos <manoskouk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72975}