Aggregate demands on zellij’s API (mostly for better UX)

[Zykino]

Features:

• Add cd and export the $CWD [FR: plugin API] zellij-org/zellij#2869
• Add a way to "give a pane" to some functions [FR: plugin API] zellij-org/zellij#2870
• Expose some user preferences ($SHELL and $EDITOR) [FR: plugin API] zellij-org/zellij#2871
• Get state before executing fn pipe [FR: plugin API] zellij-org/zellij#3580
• Pane/Tab/Session picker [FR: plugin API/contract] zellij-org/zellij#3583

Bugs:

• zellij pipe command (at least) try to parse in its <PAYLOAD> part (after --) zellij-org/zellij#3577