Expose the SVG path normalizer in SVGPathParser.h

Rename the internal NormalizingConsumer to SVGPathNormalizer and move
the class declaration to SVGPathParser.h. This will allow simplifying
the "path processor" (SVGPathParser) a bit in later CLs.
Also modify the normalizer so that it normalizes into a new
PathSegmentData, to make it more "stackable" and reusable.

BUG=467592

Review URL: https://codereview.chromium.org/1472853005

Cr-Commit-Position: refs/heads/master@{#361199}