WIP: Add more typing to instantiator

[madig]

Still need to deal with

Lib/fontmake/instantiator.py:468: error: Incompatible types in assignment (expression has type "int", variable has type "Optional[WidthClass]")
Lib/fontmake/instantiator.py:632: error: Returning Any from function declared to return "int"
Lib/fontmake/instantiator.py:638: error: Returning Any from function declared to return "int"

This is coming from ufoLib2 types. Still need to see what I can do about them. Also need to add typing to fontTools's otRound.