plugins: add workbench.action.openSettings

Fixes #7317

The following commit adds the `workbench.action.openSettings` command
so that it can be executed successfully by VS Code extensions.

Signed-off-by: vince-fugnitto <vincent.fugnitto@ericsson.com>

packages/plugin-ext-vscode/src/browser/plugin-vscode-commands-contribution.ts

@@ -202,6 +202,9 @@ export class PluginVscodeCommandsContribution implements CommandContribution {
         commands.registerCommand({ id: 'workbench.action.quickOpen' }, {
             execute: () => this.quickOpen.open('')
         });
+        commands.registerCommand({ id: 'workbench.action.openSettings' }, {
+            execute: () => commands.executeCommand(CommonCommands.OPEN_PREFERENCES.id)
+        });
         commands.registerCommand({ id: 'default:type' }, {
             execute: args => {
                 const editor = MonacoEditor.getCurrent(this.editorManager);