Fix issue preventing drag-and-drop files into Explorer view (#6030)

This change addresses an issue that prevents file drag-n-drop from
working in the Explorer view.

The problem was that there was no Electron implementation of the
accessors that Posit Workbench uses to check for file upload/download
permissions. Consequently, in desktop mode these accessors did not work.

The fix is to add accessors to the native (Electron) version of the
environment service.

Addresses #5266.


### Release Notes

#### New Features

- N/A

#### Bug Fixes

- Fix file drag and drop into the Explorer view (#5266) 

### QA Notes

This change doesn't touch the logic for Workbench so testing desktop
should be sufficient.

src/vs/workbench/services/environment/electron-sandbox/environmentService.ts

@@ -152,6 +152,20 @@ export class NativeWorkbenchEnvironmentService extends AbstractNativeEnvironment
 	@memoize
 	get filesToWait(): IPathsToWaitFor | undefined { return this.configuration.filesToWait; }
 
+	// --- Start Positron ---
+	// Always file downloads and uploads on Positron Desktop. These can be
+	// disabled in browser mode for security reasons (see
+	// BrowserWorkbenchEnvironmentService), but are always enabled in the
+	// desktop/Electron configuration.
+	get isEnabledFileDownloads(): boolean {
+		return true;
+	}
+
+	get isEnabledFileUploads(): boolean {
+		return true;
+	}
+	// --- End Positron ---
+
 	constructor(
 		private readonly configuration: INativeWindowConfiguration,
 		productService: IProductService