IDL compiler: [PerWorldBindings] for overloaded methods & simplify loops

Adds [PerWorldBindings] for overloaded methods, and simplifies the
[PerWorldBindings] loop handling, eliminating a loop in the Python template
and replacing 5 redundant branches in the Perl CG with 1 branch and 1 loop.

BUG=239771

Review URL: https://codereview.chromium.org/71093003

git-svn-id: svn://svn.chromium.org/blink/trunk@161891 bbb929c8-8fbe-4397-9dbb-9b2b20218538