Recurse into directories to find fonts. [DO NOT MERGE]

We now recurse into directories to find all fonts. This change is needed
to prevent having to list all fonts in external/google-fonts
individually.

As a side effect, we now only copy xml files over.

Change-Id: Ifdea3b8451878c2449ac7c5e17ef3d1b00d1b955
(cherry picked from commit c6364fd90de1600526d3431ce0740b6b856e48f0)