Keep file path used to create SkTypeface in MinikinFontSkia

This is a ground work for the itemize API. The file path will be the
output of the itemize API.

Bug: 114479228
Test: minikin_tests
Test: hwui_unit_tests (only tested on 32bit. couldn't test 64bit)
Change-Id: I70252594889175bf5fa0013bbaa95c6c87ca5680