vim: Support keybinding `z.` (#8702)

`z.` is similar to zz but moves the cursor to the first non-blank
character.

From the documentation:
```
z.   Redraw, line [count] at center of window (default cursor line). Put cursor at first non-blank in the line.
zz   Like "z.", but leave the cursor in the same column.
```

Release Notes:

- Support the `z.` vim keybinding: Center cursor in window and put
cursor at first non-blank