Interactive window accessibility issues for SR users

[meganrogge]

cc @jooyoungseo

1. select some code in an editor
2. use the context menu to Run In Interactive Window
3. the focus does not move to the interactive window and nothing is announced
4. if one navigates to the interactive window, there's no aria label in the input box and no info about how to reach the cells

We should:

• REPL editor - play accessibility signals to indicate execution #229181
• REPL editor - allow sending focus to the added cell when executing from another file #229182
• REPL editor - add an accessibility help dialog #229180
• REPL editor hint to open the accessibility help dialog #229178
• REPL editor - have an easy way to navigate from the input to the cells and vice versa #229177