This CL introduces a JSAny type for user-exposed JavaScript values and
a few new types to define it. Especially, it splits Symbol into
PrivateSymbol (not exposed) and PublicSymbol (JavaScript exposed
symbols).

The change is mostly mechanical, but a few things are interesting:
- PropertyKey and JSPrimitive were designed to coincide with the spec
  notions of IsPropertyKey() and primitive value, respectively.
- Since Name is an open type, we define AnyName to be the known
  subtypes of Name. This is not too elegant, but by using AnyName
  instead of Name, typeswitch can properly conclude something if a
  subtype of Name is excluded.

Small drive-by changes, which were necessary:
- Allow subtyping on label parameters.
- Fix the formatting of typeswitch, it was broken with union types
  in case types.

Bug: v8:7793
Change-Id: I14b10507f8cf316ad85e048fe8d53d1df5e0bb13
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1735322
Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63114}