In the process:

* Rework the Torque definition of ScopeInfo to enable direct
  field-style access of ScopeFlags, removing some dead code in
  the process.
* Allow implicit FromConstexpr conversion from subtypes of
  'constexpr A' to other types. This makes it possible/easy to
  convert constexpr versions of enums to other types, since the
  constexpr version of the enum isn't addressable. It's namespace
  isn't a valid namespace and is an implementation detail anyway.
* Cleanup LanguageMode: Language mode is now an enum and directly
  mirrors the C++-side definition rather than being a Smi. With
  the changes above, a new type LanguageModeSmi is introduced
  that is the Smi representation of LanguageMode that can be
  implicitly casted from constexpr LanguageMode values.

Change-Id: I190412f95e02905f445d149883fbf1f2b8ed757b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1977159
Commit-Queue: Daniel Clifford <danno@chromium.org>
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65561}