Add change_directory command

[godalming123]

Adds a command to change the working directory to the selected text. This would make it easier to (for example) embed a file-manager in helix (#9607) with the following code:

[keys.normal]
C-f = [":new", ":insert-output pwd; ls -F1", ":goto 2"]
# Mode for the file picker, TODO activate when the user presses control-f in normal mode
# 3 roadblocks:
# - activate modes from keymaps
# - if statements so that their can be 1 key to open the directory *or* the file (out of scope for the config file maybe)
# - using the escape key in custom modes
[keys.normal."_"]
esc = [":buffer-close!"]
f = ["extend_to_line_bounds", "goto_file", ":buffer-previous", ":buffer-close!"]
h = [":change-current-directory ../", "select_all", "delete_selection", ":insert-output pwd; ls -F1 --indicator-style=none", ":goto 2"]
d = ["extend_to_line_bounds", "change_directory", "select_all", "delete_selection", ":insert-output pwd; ls -F1", ":goto 2"] # Changes the current working directory to the directory under the cursor
j = "move_line_down"
k = "move_line_up"

Note that this PR only has the code, documentation still needs to be written

I plan to add a command to change the current mode in a subsequent PR so that pressing control-f could automatically open the normal."_" mode, and from that mode when a key is pressed the mode does not have to exit because it can change the mode to itself againt (tommorow maybe)

[kirawi]

If I'm understanding this correctly, you would be able to achieve this with #4709 using existing commands. However, I also know people use tmux/zellij to send keystrokes to Helix to do this kind of stuff too #8314 #2177

[the-mikedavis]

This seems like a hack around not having macro keybindings #1383 - you would use :cd <C-r>"<ret> instead. We don't generally accept 'bandaid' fixes around missing features and I don't see this command being useful once macro keybindings or scripting is possible: you would use :cd and registers interactively (i.e. outside of keybindings).

[godalming123]

See #9607 (reply in thread)