feat: move selection lines up and down

[nobriot]

Introduce a command allowing to move lines with selections up or down.

I personally liked being able to move lines without having to yank or delete and paste.
I tried something like this in the config:

up = [
  "extend_to_line_bounds",
  "yank_main_selection_to_clipboard",
  "delete_selection",
  "move_line_up",
  "move_line_up",
  "paste_after",
  "keep_primary_selection",
]
down = [
  "extend_to_line_bounds",
  "yank_main_selection_to_clipboard",
  "delete_selection",
  "paste_after",
  "keep_primary_selection",
]

but it's totally broken and works only in some limited cases, it also modifies the selection and the clipboard.

So I've added a command for it.
It's implemented it to move the lines before, after the selection. e.g. to move the selected lines 2. and 3. down, we move line 4 before the selection.

  1.         1.
 |2.   =>    4.
 |3.        |2.
  4.        |3.

It gets a bit messy when multiple selections are present.
a count can be specified. If moving up, it will be capped to the top of the file.
If moving down, additional line returns are inserted after the last line.

[mi2ebi]

duplicate functionality of #14121

[nobriot]

duplicate functionality of #14121

Okay, sorry for the noise then 🙂
Should I close the PR?