Added loading to dropdowns (#12214)

* Added loading prop to dropdowns

* Added property for setting loading text message

* removed unnecessary sets

* changed code to match new changes

* Changed the dropdown loader to use select component instead of edit.
Added missing props in dropdown loader

src/sql/azdata.proposed.d.ts

@@ -6,6 +6,7 @@
 // This is the place for API experiments and proposal.
 
 import * as vscode from 'vscode';
+import { LoadingComponentProperties } from 'azdata';
 
 declare module 'azdata' {
 	/**
@@ -256,6 +257,9 @@ declare module 'azdata' {
 		withProps(properties: TPropertyBag): ComponentBuilder<TComponent, TPropertyBag>;
 	}
 
+	export interface DropDownProperties extends LoadingComponentProperties {
+	}
+
 	export interface RadioCard {
 		id: string;
 		descriptions: RadioCardDescription[];