genlang: Explicitly decompose all display strings
We already have pretty solid support for glyph combining, so this will
allow us to utilize that to fill in gaps of our font coverage. This is
most notable for Vietnamese, Turkish, and numerous other latin-based
writing systems that have unique glyphs that are essentially just a
"standard" ascii letter plus a diacritic mark.
This leaves *voice* strings fully composed/normalized.
It also has no effect on user-supplied strings (eg filenames or file
metadata)
When we eventually utf8proc merged, this can be removed in favor
of always doing the [de]composition in-system. We will also need
to revisit our diacritic tables to ensure there's nothing missing.
Change-Id: I7012d27010bb33fb0b565ac7dfd57a16bdcad34f