Chasing method names in assignment should take operator into account

[mozfreddyb]

This is a follow-up from #207 and #206.
The patch fixed working with function calls in code like (a = b)(foo), but did not take the assignment operator into account.

A simple equal sign will ensure that only b will ever be called, as it is assigned into a.
However, operators like ||= will not.

[mozfreddyb]

Turns out this will require a bit of a refactor.
Currently, this comes up in normalizeMethodName() which is supposed to return one method name as the normalized name. However, in case of a call like a ||= b)(foo) the function that's called is either a or b, so we need to check both..