Previously, arrow function scopes had a separate ScopeType. However,
Scope::DeserializeScopeChain() erroneously deserialized ARROW_SCOPE
ScopeInfos as FUNCTION_SCOPE. This could lead to bugs such as the
attached one, where "super" was disallowed where it should have
been allowed.

This patch utilizes the Scope's FunctionKind to distinguish arrow
functions from others. Besides fixing the above bug, this also
simplifies code in various places that had to deal with two different
ScopeTypes both of which meant "function".

BUG=v8:4466
LOG=n

Review URL: https://codereview.chromium.org/1386253002

Cr-Commit-Position: refs/heads/master@{#31154}