This CL shuffles around some code in `ScopeIterator` to better reflect
the two (internal) iteration modes:

  - While "inside" the paused function we iterate based on lexical
    scopes.
  - Once we move past the paused function we iterate based on runtime
    contexts.

This CL renames the advancing functions to `AdvanceScope` and
`AdvanceContext` respectively which operate in the following way:

  - `AdvanceScope` first checks if the current lexical scope requires
    a context. If so, we move one context up the chain, since the next
    lexical scope belongs to that next context. Then we move up one
    lexical scope.

  - `AdvanceContext` moves one context up the context chain. Then we
    we move up through all the lexical scopes until we find the next
    lexical scope that requires a context.

The tricky bit is the transition from scope iteration mode to context
iteration mode. This is where the bug fix comes in. After doing one
standard `AdvanceScope` from the `closure_scope_` to the next
lexical scope, we need to keep moving up through the lexical scope
until we find the next lexical scope that requires a context.

The CL also changes how we collect the locals blocklist. The
locals blocklist is always put on the current context. So every
time we move up one context we reset the locals blocklist and
every time we move up the lexical scope we collect the scope
locals into the blocklist.


R=bmeurer@chromium.org, jarin@chromium.org

Fixed: chromium:1354464
Change-Id: I7b37687a8827c20d0660a25413d2c9117b5fe5ba
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3842158
Commit-Queue: Simon Zünd <szuend@chromium.org>
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82615}