Moving Text Simple/Complex Path prefix from Font.cpp to new File

Moving Text/String Path emum to new file "TextPath.h", this is
done inline with the comments given in "https://codereview.chromium.org/111833006/"
which required breaking commit to two.

BUG=330832

Review URL: https://codereview.chromium.org/116423007

git-svn-id: svn://svn.chromium.org/blink/trunk@164745 bbb929c8-8fbe-4397-9dbb-9b2b20218538