Desktop interface should allow accessing to recent files and xdg dirs

[Marco Trevisan (Treviño)]

With desktop interface + home readability, a snap should be able to read ~/.local/share/recently-used.xbel and ~/.config/user-dirs.* to properly setting up the file-open dialog (as not all the apps will use portals initially).

[Marco Trevisan (Treviño) (3v1n0)]

Desktop launcher should then read ~/.config/user-dirs.dirs and, if it has access to the real user home, redefine the various XDG_* dirs with those paths.

[Zygmunt Krynicki (zyga)]

I agree that it would be good if part of the execution chain could read the XDG directories and at least set the variables.

I would vote on snap run, because:

 - it runs without confinement so it can read those files
 - it is written in go so should be easier to write correct and safe code

The trick is how to do it exactly: should those always be set? Unfortunately snap run doesn't know if a particular interface is connected or not.

I'm marking this bug as triaged.