bug#66732: tree-sitter fontification doesn't update multi-line syntax reliably

[Stefan Monnier]

>> It seems like in our scenario the region does not get re-rendered even 
>> when some of the faces changed in there.
> Can't happen.

I think Dmitry is talking about the case where the faces were change
after the text was rendered (but before the end of the redisplay cycle).

I.e. the redisplay starts, renders up to position POS, then calls
jit-lock because `fonfitied` is nil, and jit-lock modifies faces of text
*before* POS.


        Stefan