RFC: Include some way for autohide panels to be forced open by other clients (Use case/idea in description)

[ryanabx]

This is a complex ask, but the reason I'd like to have a way for autohide panels to open for some toplevels is so that we can have the panel open when cosmic-app-library or cosmic-workspaces is open:

It'd also need to be possible for those apps to see the "exclusive zone" this autohide panel would take up if it were a static panel