Add rootFolderNames & rootFolderNamesExpanded iconThemes definitions for root folders

[harbin1053020115]

We need to custom iconThemes of the workspace's root folders, we want to custom different iconThemes for each root folders according to the root folder's name:

[aeschli]

fixed by #195319

[aeschli]

To verify:

• create a new file icon theme. You can use https://github.com/microsoft/vscode/tree/main/extensions/theme-defaults/fileicons as an example
• add properties rootFolderNames & rootFolderNamesExpanded

[DonJayamanne]

Gave it a good crack, but unable to get things working.
Hopefully someone else will have better luck

[joaomoreno]

Gave it a good crack, but unable to get things working. Hopefully someone else will have better luck

@DonJayamanne, can you provide @aeschli with details where you got stuck, so he knows how to improve the verification steps next time? Thanks.