Handle coding ligatures

[pokey]

Currently cursorless decorations don't play nicely with fonts with coding ligatures. We could:

• Use something like this to detect if user font has various ligatures
• If so, treat the whole ligature as one character
• Then user would have to map those ligature strings as symbols to use in decorated marks on talon side. So they'd say eg "take triple equal" and talon would pass through "===" as the symbol, instead of passing through only single chars like it does today
• We'd then need to make sure that hats center properly over these ligatures. I guess we could measure them when we're looking for them in the first place

[pokey]

81 proposes a simpler solution, which might be a decent place to start