Notebook StdIn support to fix #5231 (#5232)

Fixes #5231 
- Add stdin handling. Has to be at UI level so add plumb through handling
- Add unit tests
- Add new StdIn component.

Testing:
Unit Tests and manual testing of following:
- Prompt for password using `getpass` in python.
   - Password prompt is hidden since "password" is true.
   - Hit enter, it completes
- prompt, stop cell running, StdIn disappears
- prompt, hit escape, stdIn disappears and stdIn request is handled.

Issues: focus isn't always set to the input even though we call focus.
Will investigate this further.

src/sql/azdata.proposed.d.ts

@@ -5110,6 +5110,10 @@ declare module 'azdata' {
 		 */
 		export interface IStdinMessage extends IMessage {
 			channel: 'stdin';
+			content: {
+				prompt: string;
+				password: boolean;
+			};
 		}
 
 		/**