[SVG] Base classes for new SVGAnimatedProperty/TearOff implementation.

This patch introduces base classes of new SVG animated property and tear-offs implementation, and add support for them.
The new classes are introduced with "New" prefix, but these prefixes are to be removed when migration of all animated property types are done to use new implementation.

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

BUG=308818

Review URL: https://codereview.chromium.org/111933008

git-svn-id: svn://svn.chromium.org/blink/trunk@164004 bbb929c8-8fbe-4397-9dbb-9b2b20218538