IDL compiler: add sequence<Dictionary> argument and simplify type handling

This syncs to r162335:
Add Perl IDL support for method parameter type sequence<Dictionary>
https://codereview.chromium.org/74533003/

...and significantly simplifies the type handling in V8 -> C++ conversions,
by putting all the logic in includes_for_types, instead of splitting it
between includes_for_types and v8_value_to_cpp_value.
This simplifies dicts as well (simple type -> conversion, without also
listing includes) and thus lets us merge 2 dicts (basic types and interface
types).

BUG=257235
BUG=239771
NOTRY=true

Review URL: https://codereview.chromium.org/79223005

git-svn-id: svn://svn.chromium.org/blink/trunk@162446 bbb929c8-8fbe-4397-9dbb-9b2b20218538