IDL compiler: Overloaded methods: type checking

This starts type checking for overloaded methods.
Some Perl changes to make the generated code more consistent,
simplifying the CGs, especially the Python.
(This makes simple checks have extra parens,
 though the generated code for resolution checks
 are pretty illegible anyway.)

BUG=239771

Review URL: https://codereview.chromium.org/70053002

git-svn-id: svn://svn.chromium.org/blink/trunk@161796 bbb929c8-8fbe-4397-9dbb-9b2b20218538