Factor formal argument parsing into ParserBase

Factor formal argument parsing into ParserBase

This commit is a precursor to making lazy arrow function parsing use
similar logic to function(){} argument parsing.

Originally landed in these three CLs:

  https://codereview.chromium.org/1078093002
  https://codereview.chromium.org/1083623002
  https://codereview.chromium.org/1083953002

These were rolled out due to a performance regression on CodeLoad.  This
patchset will fix that by avoiding creation of a DuplicateFinder in the
full parser.

R=marja@chromium.org
BUG=
LOG=N

Review URL: https://codereview.chromium.org/1100713002

Cr-Commit-Position: refs/heads/master@{#27960}