Get rid of SVGPoint special case from the bindings generator

Get rid of SVGPoint special case from the bindings generator by adding a
new SVGPoint.h header that contains a typedef to FloatPoint.

Also use SVGPoint type in the implementation API for consistency with
the IDL.

Review URL: https://chromiumcodereview.appspot.com/18098007

git-svn-id: svn://svn.chromium.org/blink/trunk@154164 bbb929c8-8fbe-4397-9dbb-9b2b20218538