[vscode] test and fix bogus param combinations to open dialogs

[akosyakov]

Right now there seem to be missing cases for open dialogs when they are called from VS Code extensions. It would be good to set up a small VS Code extension contributing several commands with different options combinations, run it against Theia and VS Code side by side and fix missing cases and differences.

Motivated by #4763

[benoitf]

hello, could you list your current missing case ?

[benoitf]

sorry, hit enter too soon. I wanted to bring source data in the notification. Is it part of your issue ?

[akosyakov]

My problem that there is no way to verify right now that there are no such cases. Looking at the code we don't have internal clients for some combinations and i doubt they work properly called from VS Code extensions. i.e. with disable canSelectFolders but enabled multiple selection it can leak actually folders.

[vzhukovs]

@akosyakov I think, that here check condition should be improved to verify whether property canSelectFolders is not undefined. Because user can omit this property and value !undefined will be true.

[akosyakov]

@vzhukovskii ok, but we really need tests, not fixing it blindly, another possible dialog issue: #4820 (comment)