Problem:
InsertCharPre is triggered for stuffed text (".", i_CTRL-R, i_CTRL-A).
But that text was already transformed when it was typed: the `v:char`
result is appended to the redo buffer literally (`redo_append_lit()`).
So "." transforms it again, e.g. an autopair handler turns "()" into
"())".
Solution:
Skip InsertCharPre for stuffed text.
Precedent: `vgetorpeek()` disables abbreviations for stuffed text for
the same reason (it is post-expansion).
Macros are unaffected.
8c292c96dd
