linux: Show warning if file picker portal is missing (#14401)

This PR adds a warning when the file chooser couldn't be opened on Linux

It's quite confusing when trying to open a file and apparently nothing
happens:

fixes https://github.com/zed-industries/zed/issues/11089,
https://github.com/zed-industries/zed/issues/14328,
https://github.com/zed-industries/zed/issues/13753#issuecomment-2225812703,
https://github.com/zed-industries/zed/issues/13766,
https://github.com/zed-industries/zed/issues/14384,
https://github.com/zed-industries/zed/issues/14353,
https://github.com/zed-industries/zed/issues/9209


![image](https://github.com/user-attachments/assets/5acabdaa-7a9d-4225-9480-e371d20387c3)


Release Notes:

- N/A
f3ddd18201apricotbucket28 committed on 7/15/2024, 4:36:39 PM· committed by GitHubparent5d860e2
11 files changedLine totals unavailable