Allow selecting only directories from a `data-url`\`file` widget

[TheOneTheOnlyJJ]

Prerequisites

• I have read the documentation

What theme are you using?

core

Is your feature request related to a problem? Please describe.

I want a data-url widget that allows users to select only directories.
I have not found any way to do it as of now.

Describe the solution you'd like

A new widget or UI Schema prop should be added that allows the user to select a directory instead of a file (or more).
This may have to wait until showDirectoryPicker becomes Baseline Newly Available.

Describe alternatives you've considered

I haven't come up with any alternative to this.
The input element does not seem like it accepts selecting directories in any way as of now.

[nickgros]

@TheOneTheOnlyJJ Could you do this with a custom FileWidget override, assuming you only target browsers that support showDirectoryPicker?

[TheOneTheOnlyJJ]

I opened this issue as I see directory selection as a good potential feature for the library.
My project in question is a local-first Electron.js app, so the Electron-specific APIs also offer local filesystem access.
I will build my own custom solution, which I will happily share when I get around to doing it.