feat(panes): allow specifying coordinates for a new floating pane through the CLI or plugins

[imsnif]

This adds the must requested feature of specifying coordinates (x, y, width, height) for floating panes opened from the CLI with the various new_pane commands (zellij run, zellij edit, zellij plugin, etc.) as well as through the plugin API.

Coordinates can be specified either in fixed numbers (eg. 1) or percentages (eg. 25%).

Example:

# opens a new floating pane running "cargo test" at the specified coordinates
zellij run --floating -x 10 -y 25% --width 100% --height 20% -- cargo test

All of these coordinates are optional, omitting some of them will merge them with the default location for the next pane according to the currently active swap layout. Coordinates that exceed the viewport will be truncated on a best-effort basis.