When a command used an explicit register (e.g. `"_dd` or `"add`), the
subsequent dot repeat (`.`) was ignoring that register and using the
default instead.

Store the register at recording start in `recording_register_for_dot`,
persist it to `recorded_register_for_dot` when recording stops, and
restore it in `Vim::repeat` when no explicit register is supplied for
`.`. An explicit register on `.` (e.g. `"b.`) still takes precedence.

This commit also updates the dot-repeat logic to closely follow Neovim's
when using numbered registers, where each dot repeat increments the
register. For example, after using `"1p`, using `.` will repeat the
command using `"2p`, `"3p`, etc.

Closes #49867

Release Notes:

- Fixed vim's repeat . to preserve the register the recorded command
  used
- Updated vim's repeat . to increment the recorded register when using
  numbered registers

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Co-authored-by: dino <dinojoaocosta@gmail.com>