When text is completed, new_text contains the entire new completion
which replaces the old_text. In Vim mode, pressing . repeats the
completion; if InputHandled records the full text and no range to
replace, the entire completion gets appended; this happens after the
completion prefix typing repeats, and we get a duplicate prefix.
Using range to replace has some downsides when the completion is
repeated as a standalone action; in a common case, it should be
sufficient to record the new suffix. This is actually what used to
happen before #28586, which removed this code in a larger attempt to fix
completions at multiple cursors:
```rust
let text = &new_text[common_prefix_len..];
let utf16_range_to_replace = ...
cx.emit(EditorEvent::InputHandled {
utf16_range_to_replace,
text: text.into(),
});
```
Fixes#30758Fixes#31759Fixes#31779
Release Notes:
- Vim: Fix duplicate prefixes when repeating completions via `.`
e0b818af62