- Directly declares the special catch variable from the parser-base.
- Tracks Scope on PreParserBlock and finds conflicting lexical declarations by
  simply walking the VariableMap of the block inserted for the pattern; or the
  catch variable in case of identifier.
- This also enables throwing errors for duplicate let in the preparser. We may
  have to back that out if it breaks something.

Bug: v8:2728, v8:7828
Change-Id: Id2eea62062533eb99cd6670c42a4b1da87139008
Reviewed-on: https://chromium-review.googlesource.com/c/1382095Reviewed-by: Igor Sheludko <ishell@chromium.org>
Commit-Queue: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58353}