Until now we've only exposed trace output for the parse- and assembly
stages of regexp codegen. Debug tracing of the graph was missing. The
new --trace-regexp-graph flag fills that hole.

Available regexp codegen tracing flags are now:

--trace-regexp-parser
--trace-regexp-graph
--trace-regexp-assembler

The output of --trace-regexp-graph can be formatted with `dot`, for
example:

 $ d8 --trace-regexp-graph [...] | dot -Tjpg -o regexp-graph.jpg

Change-Id: Ice593c34f7818c94e42d98e98a31533178bb538b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2808945
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Auto-Submit: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Patrick Thier <pthier@chromium.org>
Cr-Commit-Position: refs/heads/master@{#73825}