Move font xml files to "standard" directory

This will allow to load different fonts for standard and native versions
of layoutlib.

Exempt-From-Owner-Approval: layoutlib branch
Bug: 143073883
Test: N/A
Change-Id: If44fc587eac2c3543cdff3760e64df003f12bdf2
(cherry picked from commit a9c9c7410491c42733ab565ca75a8708d4a9b064)