[pgAdmin4][Patch]: RM # 2895 - All the controls and display elementsin the main window to be accessible using the tab key in an appropriate order

Please find the attached patch for RM #2895: As a keyboard user who has difficulty using a mouse, I need all the controls and display elements in the main window to be accessible using the tab key in an appropriate order.

Key Notes:

1. While loading the application, all the focusable objects are accessible (Main menu, Right Panel, Left Panel)

1. Left hand side tree view is accessible via Alt+Shift+B

2. Right side tabbed panels are accessible via Alt+shift+[  and Alt+shift+]

3. Main menu navigation

    File Menu - Alt+Shift+F

    Object Menu - Alt+Shift+O

    Tools Menu - Alt+Shift+L

    Help Menu - Alt+Shift+H

4. Once the menu is opened, user can access the next/previous main menu through the left and the right arrow keys 

5. When the user is in the SQL Editor and wants to change the panel, use ESC key to move the cursor out from the text editor and then can use the default shortcut keys (Alt+Shift+[ / Alt+Shift+])

Thanks,

Khushboo