Add a "combination" assert scope class, which combines multiple existing
assert scopes.  This will allow scopes with functional overlap, e.g.
DisallowGarbageCollection and DisallowHeapAllocation, to share an assert
type rather than rather than requiring users to remember to set both. To
demonstrate this, this redefines DisallowGarbageCollection to a
combination of DisallowHeapAllocation and a new DisallowSafepoints, and
some of the DCHECKs checking both are simplified to only check one or
the other, as appropriate.

The combination classes become subclasses of the existing assert scopes,
so that they can be used in their place as e.g. a function parameter,
e.g. DisallowGarbageCollection can be passed to a function expecting
const DisallowHeapAllocation&.

As a drive-by, this also changes the per-thread assert scopes to use a
bitmask, rather than a bool array, to store their per-thread data. The
per-isolate scopes already used a bitmask, so this unifies the
behaviour between the two.

Change-Id: I209e0a56f45e124c0ccadbd9fb77f39e070612fe
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2534814
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71231}