fontc producing less lookups for inline contextual liga substitutions

[cmyr]

Given the FEA,

lookup locl_latn_1 {
        script latn;
        language CAT;
        sub l' periodcentered' l by ldot;
        sub L' periodcentered' L by Ldot;
} locl_latn_1;

(from https://github.com/googlefonts/fuggles/blob/master/sources/Fuggles.glyphs)

fontc produces a single type-4 lookup with sub L periodcentered by Ldot and sub l periodcentered by ldot, but fontmake produces a different lookup for each rule.

It would be easy enough to make fontc match fontmake, but unless I'm missing something the fontc version is better; fontmake performs this same optimization in other places, just not here.

@anthrotype would it be much work to add this in fontmake?

edit: opened fonttools/fonttools#3701 to discuss addressing this in fonttools