Allow coloring individual files in the explorer view using the context menu

[VSCodeTriageBot]

https://github-com/user-attachments/assets/5ba79f23-25ea-418b-8822-9e1017b4f9c2

Select individual files with the context menu and set a background color on them. The background colors / list can be saved to the .vscode folder so they're persistent in the project and can be shared with others.