Support multiple languages per font in fonts.xml

Minikin already supports multiple languages specified per font in
I7f13b51464c9b01982bb573251d77052b9ddbd70. This CL adds a couple of
such cases into fonts.xml and clarifies in the method and the
variable names and parameters that the frameworks is handling a
multi-language string when it is.

Fixes: 26687969
Test: make -j checkbuild
Test: bit FrameworksCoreTests:android.graphics.TypefaceSystemFallbackTest
Change-Id: Ifa540a95f87921983f9069330d1dd0892538a8df