This is a reland of 0ba115e6
Changes compared to last reland:
- Fix Python code trying to write to expected_outcomes, which is now a
  computed property.
- Fix remaining place in d8.cc that ignored the --fuzzing flag.
- Expect flag contradictions for --cache in code_serializer variant.

Original change's description:
> Reland^3 "[flags] warn about contradictory flags"
>
> Changes:
> - Also allow second parameter influenced by --cache to be reassigned.
> - Fix --stress-opt to only --always-opt in the last iteration as before.
>
> Original change's description:
> > Reland^2 "[flags] warn about contradictory flags"
> >
> > This is a reland of d8f8a7e2
> > Change compared to last reland:
> > - Do not check for d8 flag contradictions in the presence of --fuzzing
> > - Allow identical re-declaration of --cache=*
> >
> > Original change's description:
> > > Reland "[flags] warn about contradictory flags"
> > >
> > > This is a reland of b8f91666
> > > Difference to previous CL: Additional functionality to specify
> > > incompatible flags based on GN variables and extra-flags, used
> > > to fix the issues that came up on the waterfall.
> > >
> > > This also changes the rules regarding repeated flags: While
> > > explicitly repeated flags are allowed for boolean values as long
> > > as they are identical, repeated flags or explicit flags in the
> > > presence of an active implication are disallowed for non-boolean
> > > flags. The latter simplifies specifying conflict rules in
> > > variants.py. Otherwise a rule like
> > >
> > > INCOMPATIBLE_FLAGS_PER_EXTRA_FLAG = {
> > >   "--gc-interval=*": ["--gc-interval=*"],
> > > }
> > >
> > > wouldn't work because specifying the same GC interval twice
> > > wouldn't actually count as a conflict. This was an issue with
> > > test/mjsunit/wasm/gc-buffer.js, which specifies
> > > --gc-interval=500 exactly like the extra flag by the stress bot.
> > >
> > > Also, this now expands contradictory flags checking to d8 flags
> > > for consistency.
> > >
> > > Original change's description:
> > > > [flags] warn about contradictory flags
> > > >
> > > > Design Doc: https://docs.google.com/document/d/1lkvu8crkK7Ei39qjkPCFijpNyxWXsOktG9GB-7K34jM/
> > > >
> > > > Bug: v8:10577
> > > > Change-Id: Ib9cfdffa401c48c895bf31caed5ee03545beddab
> > > > Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2154792
> > > > Reviewed-by: Clemens Backes <clemensb@chromium.org>
> > > > Reviewed-by: Michael Achenbach <machenbach@chromium.org>
> > > > Reviewed-by: Georg Neis <neis@chromium.org>
> > > > Reviewed-by: Tamer Tas <tmrts@chromium.org>
> > > > Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
> > > > Cr-Commit-Position: refs/heads/master@{#68168}
> > >
> > > Bug: v8:10577
> > > Change-Id: I268e590ee18a535b13dee14eeb15ddd0a9ee8341
> > > Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2235115
> > > Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
> > > Reviewed-by: Tamer Tas <tmrts@chromium.org>
> > > Reviewed-by: Clemens Backes <clemensb@chromium.org>
> > > Reviewed-by: Georg Neis <neis@chromium.org>
> > > Cr-Commit-Position: refs/heads/master@{#68989}
> >
> > Bug: v8:10577
> > Change-Id: I31d2794d4f9ff630f3444210100c64d67d881276
> > Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2339464
> > Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
> > Reviewed-by: Clemens Backes <clemensb@chromium.org>
> > Cr-Commit-Position: refs/heads/master@{#69339}
>
> Bug: v8:10577
> Cq-Include-Trybots: luci.v8.try:v8_linux64_tsan_rel_ng
> Cq-Include-Trybots: luci.v8.try:v8_linux64_tsan_isolates_rel_ng
> Change-Id: I4a69dc57a102782cb453144323e3752ac8278624
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2352770
> Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
> Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
> Reviewed-by: Clemens Backes <clemensb@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#69433}

Change-Id: Ib6d2aeb495210f581ac671221c265df58e8e5e70
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2398640
Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Tamer Tas <tmrts@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69954}