We usually run benchmarks in multiple variants: default, future, noopt
This is currently only achieved by copying the run-perf json file and
changing the flags at the top-level (or copy whole subsections).

Using "variants" we can duplicate the tests at the current level with
different values and easily create benchmarks that differ only in v8
flags.

Drive-by-fix:
- Add Node.__iter__ and log the whole config graph in debug mode
- Add GraphConfig.__str__ method for better debugging
- Rename TraceConfig to LeafTraceConfig
- Rename RunnableTraceConfig to RunnableLeafTraceConfig
- Make --filter accept a regexp to better filter out variants

Bug: v8:12821, v8:11113
Change-Id: I56a2ba2dd24da15c7757406e9961746219cd8061
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3596128Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Tamer Tas <tmrts@chromium.org>
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/main@{#80307}