Explorer: Use compressed tree widget

[joaomoreno]

Implements #41627

TODO

• Creating a new top-level file/folder seems to erase compression data
• Expose compressionEnabled tree/model option
• Expose this to the user via a explorer.compressSingleChildFolders setting

[joaomoreno]

OK merging this barebones implementation, including a explorer.compressSingleChildFolders setting:

@isidorn Here are next steps, if you plan on advancing this:

• Handle each folder in a compressed tree node separately. One should be able to hover the folder names and drag them or context menu click them and get the actions only for that folder. One should also be able to drop files selectively on each folder.
• The explorer.compressSingleChildFolders setting could be a resource setting and be scoped per folder, ie each root folder could have different compression settings, for example. Compression can only be enabled/disabled globally per tree right now. But the isIncompressible method will give you finer level of control allowing you to implement this.

[isidorn]

Fancy! Great work. I am still buried in notifications, but we can sync tomorrow / thursday so we talk about how to split up the rest of the work. Thanks