IDL compiler: [CallWith] for methods (void, no optional arguments)

This provides basic [CallWith] support, with some refactoring.
(Shared attribute/method code is now v. small, since most isn't
 relevant for both.)

non-void methods and optional arguments both require significant
additional work, so will do in followup CLs.

BUG=239771
NOTRY=true

Review URL: https://codereview.chromium.org/59033003

git-svn-id: svn://svn.chromium.org/blink/trunk@161317 bbb929c8-8fbe-4397-9dbb-9b2b20218538