If the post subset cmap12 table is equivalent to another cmap subtable don't include the 12 table in the final subset. Matches change https://github.com/fonttools/fonttools/pull/2146 from fontTools.
- subset class def 1 against the coverage table.
- Don't re-use class 0 in class def 2.
- Ignore class 0 glyphs for the purposes of determing format 1 vs format 2 encoding for ClassDef.
Add an additional test case which demonstrates these issues.
Garret Rieger
Qunxin Liu