SVG rendering ignores xml:space="preserve" attribute for text

Make tspan and textPath inherit the css-whitespace property by default. This means it will either use the
same xml:space setting as its parent text container, or use its own xml:space value if provided.

This actually fixes text-tspan-02-b.svg.

BUG=231508

Review URL: https://codereview.chromium.org/166673006

git-svn-id: svn://svn.chromium.org/blink/trunk@167393 bbb929c8-8fbe-4397-9dbb-9b2b20218538