Do not accept drop if location is unmounted

[jeremypw]

Fixes #2390
Fixes #2465

• file_accepts_drop () returns false if location unmounted (fixes first issue)
• Update the target location if mounted after Files started (fixes second issue)

[danirabbit]

Can you resolve conflicts? It looks like maybe this function moved in another commit

[jeremypw]

Conflict fixed

[danirabbit]

@jeremypw ah this is a +/-0 diff now 😅 That doesn't seem right

[jeremypw]

Looks like libcore/FileUtils/file_accepts_drop function was moved elsewhere in main so need to rewrite this branch if the issue persists.

[jeremypw]

Noticed a related issue - the volume bookmarks only have a valid target file if they are already mounted when Files window is opened. In main, the target file is not updated if the volume is subsequently mounted so dropping a file on it still does not work in this branch. This is now fixed by updating the target file whenever the volume is mounted or unmounted.

[jeremypw]

@danirabbit This is now ready for review hopefully.

Required changes made new review requested

[jeremypw]

Converting to draft to investigate bug where a (copy) file is created in the current working folder when Files is being run in a terminal and the file is dropped onto an unmounted volume.

[jeremypw]

For now, I have not implemented auto-mounting of unmounted volumes when dropped on. This could be implemented in a further PR if thought desirable.

[jeremypw]

Converting to draft to investigate bug where a (copy) file is created in the current working folder when Files is being run in a terminal and the file is dropped onto an unmounted volume.

I am no longer sure how to reproduce this bug so a shorter PR has been proposed omitting the related commit.

[jeremypw]

Closing in favour of #2466 and #2468