UCA: Add possibility to address items on the inactive split pane

Hello! o)

I like to ask for placeholders which represent the path / selected files in the "destination" file listing (in split view). Having "access" to the second or "destination" file listing in split view is a major functionality in file managers since.. I really miss that in Thunar! o)

Some examples of what essential feature to allow..

• run action to sync / compare folders or files in "source" and "destination"
• run action to create archives in the "destination" (because of read-only or 100% full file system in "source")
• run action to extract archives to destination (same reason as before)
• run action to create "low res" images in destination
• run action to run which requires items from "source" and "destination"

I searched this place to find a similar request, did not find anything. The current Thunar allows to use these placeholders..

Maybe the same codes / placeholders can be used for "destination" by appending a simple "d" to the existing codes? What do you think? o)

Thank you! o)

btw: Dolphin also lacks this feature and "only" implements the XDG Desktop spec, which does not support "destination" paths and items.