Use CSSValueIDs for CSSParserFunction names

This patch replaces the CSSParserString CSSParserFunction::name with a
CSSValueID id. Currently all the users of the name have to do a string
comparison, which makes the relevant parsing code comparatively messy.
Using CSSValueID here make functions behave the same way as regular
keywords.

As a result, we can now easily move the transform parsing code into the
CSSPropertyParser, which currently resides in BisonCSSParser-in.cpp due
to using the SWITCH/CASE code generation (in fact we can remove this
code generation from BisonCSSParser-in.cpp completely).

BUG=404023

Review URL: https://codereview.chromium.org/615553002

git-svn-id: svn://svn.chromium.org/blink/trunk@183017 bbb929c8-8fbe-4397-9dbb-9b2b20218538