Pass custom fallback info to minikin

The custom fallback info is used for determine the priority between
custom fallback and locale fallback. The custom fallback should be
given priority over locale fallback.

Bug: 116512426
Test: minikin_tests
Test: atest TypefaceCustomFallbackBuilderTest
Change-Id: I79cc82fa990d7705ea5c40e9b0be40d062c218dc