This is an initial (and partial) step towards full typing in graph
assembler. It removes all uses of SloppyTNode, starts to introduce
types in the GraphAssembler base class, and makes lambda function
types (for if- and for-builders) more specific.

Plenty of TODOs remain; e.g. checked casts and complete typing of
GraphAssembler are left to follow-up work.

Bug: v8:9972
Change-Id: I780adf83b53ad76beda4726960d95ab6df13e2ce
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1940476
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65241}