Improve keyboard actions in Datagrid toolbar

[elycheea]

Priority fixes

• Tabbing to previous or next item from settings popover should most likely close popover in toolbar
• Popover should close on Escape
  • Carbon uses onKeyDown in Popover Storybook example

Enhancements

These are good to fix if simple, but are lower priority given that they most likely have a workaround and can be addressed after initial release so that we can prioritize bigger fixes.

• When opening the popover with enter/space, focus should go to the first item in the popover list (radio)
  • Note: There is a workaround — users have an extra tab / up/down to navigate into the popover options
• Using arrow keys to navigate radio items should not scroll the full table

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2. When you are able to correctly open the dropdown, you must press tab again - and the faint 1px blue focus state appears around settings, - then press tab a second time to enter the list before you are able to press up/down/L/R to navigate the list. Focus should be present in the first list item after pressing space/enter to activate the popover. Also as you press up/down arrows to cycle through the radio button options, the table itself moves up and down behind it.

3. When popover is open and you tab to settings, it closes. However, if popover is open and you shift+tab to Download before interacting with the popover content, the popover remains open and overlaps with the Download tooltip. I’m thinking it should close so that what happens with shift+tab is consistent with what happens with tab.
   

4. When open, the popover should dismiss when Esc is pressed

Originally posted by @kristastarr in #3117 (comment)