IDL compiler: Static attributes for partial interfaces and [ImplementedAs] interfaces

Straightforward, just:
* using cpp_name instead of interface.name at suitable places,
* adding appropriate checks,
* ordering logic correctly.

Also:
* Remove dead code (v8_attribute copy of scoped_name)
* Reorder template slightly (order was off)

BUG=239771
R=haraken
NOTRY=true

Review URL: https://codereview.chromium.org/132233009

git-svn-id: svn://svn.chromium.org/blink/trunk@165268 bbb929c8-8fbe-4397-9dbb-9b2b20218538