Update Toaq text entry helpers for Delta

[lynn]

When adding a new lemma, or typing inside **nuımlaı**…

• - should become a prefix underdot on the last vowel.
• vy?|wy?|w should become ꝡ.
• ka4 should be converted to kâ, not kả.

[uakci]

Yeah, this is something we should be able to do. For anybody wondering, the relevant code is placed here in the awkwardly stranded frontend/shared directory.

[lynn]

Thought: Normalizing bu- to bu-underdot too universally will prevent us from entering and searching for dictionary forms of prefixes, which I believe do want the hyphen. (I thiiink a regex like -(?=\w) is right.)

[uakci]

I wouldn't mind bụ becoming the actual dictionary spelling (and since the database normalizes itself on startup, this change would not require users to edit their entries). But otherwise yeah, plus that makes some sense anyway since you cannot convert a hyphen the moment you see it (because then there'd be no way of knowing if a following vowel should be padded with an apostrophe, as in háo-ao → hạ́o'ao).

[uakci]

Note that the only replacement implemented for ⟨ꝡ⟩ in the search field (but not during composition) is ⟨vy⟩. Anything more complex than this would've required overhauling some part of the search logic (I don't really even want to begin to wonder which ones it would be), something that is out-of-budget for the time being. If this turns out to be a big usability issue then please reopen #21.