Add support for clickable links and other webview options (#2396)

* Add support for clickable links and other webview options
- Added click handling
- Added suport for localResourceRoots to be read in the webview

* Options should not be mandatory

* Ensure the constructor-defined properties are preserved
- This fixes issue where the extensionFolderPath was lost during webview withProperties call in the modelbuilder.

* enableCommandUris should be a getter

* Add position support to webview and to flexContainer

* Fix regressions on editor view caused by merge

src/sqltest/workbench/api/extHostModelView.test.ts

@@ -69,7 +69,7 @@ suite('ExtHostModelView Validation Tests', () => {
 				.component();
 			await view.initializeModel(flexContainer);
 			done();
-		});
+		}, undefined);
 
 		extHostModelView.$registerWidget(handle, widgetId, undefined, undefined);
 	});