Add inRustProject when-clause for commands.

editors/code/src/util.ts

@@ -94,3 +94,8 @@ export function isValidExecutable(path: string): boolean {
 
     return res.status === 0;
 }
+
+/** Sets ['when'](https://code.visualstudio.com/docs/getstarted/keybindings#_when-clause-contexts) clause contexts */
+export function setContextValue(key: string, value: any): Thenable<void> {
+    return vscode.commands.executeCommand('setContext', key, value);
+}