Conditional activity bar icon

[tianrui-qi]

Currently, the R extension icon always appears in the Activity Bar, regardless of whether there are any R-related files (like .R or .Rmd) in the workspace. It shows up even no file/fold is open. This can clutter the sidebar, especially when working on projects that don’t involve R. It also introduces unnecessary visual noise when the extension isn’t actively needed.

For example, the Java extension in VS Code only activates when it detects Java files in the workspace, at which point the “Testing” icon appears in the Activity Bar. Similarly, the Python extension activates when a Python file is opened, triggering the “Testing” icon to appear.