[SVG] SVGAnimatedString{,List} migration to new SVG property impl.

This CL replaces SVGAnimatedString{,List} with NewSVGProperty based implementation.

The original SVGStringList had a hack where it parsed empty string to a list with a single empty string [''], but this hack is removed.

This CL also fixes a bug in SVGTest where 'systemLanguage' constraint was always rejected when multiple languages were specified.

For details, see design doc: https://docs.google.com/document/d/1bg7CUyUszqdwmENY3JX6_PoQD6uHRCNcRPJMlC4qlkw/edit?usp=sharing

BUG=308818

Review URL: https://codereview.chromium.org/148173018

git-svn-id: svn://svn.chromium.org/blink/trunk@166227 bbb929c8-8fbe-4397-9dbb-9b2b20218538