Support "dtx" vim key combination when "x" is immediately to the right of the cursor (#6830)

Closes #4358

The bug originates on this line:
https://github.com/zed-industries/zed/blob/5db7e8f89ee4f5d9801a2eab88adc1db3fda0f46/crates/vim/src/motion.rs#L451

- When running "dtx" on "ˇabcx", the range to delete is 0 -> 2 ("abc")
- When running "dtx" on "abˇcx", the range to delete is 2 -> 2 ("c"), so
`new_point == point` and the function incorrectly returns `None` and "c"
is not deleted
- We need to disambiguate between the "not found" case and the "found
immediately to the right" case
- This bug does not apply to the backwards case ("dTx")

Release Notes:
- Fixed "dtx" vim key combination when "x" is immediately to the right
of the cursor (#4358)