[a11y] Improve WB Accessibility

[maxpatiiuk]

WorkBench Mapper is now accessible
Still need to fix the WorkBench Data Editor page:

• All actions should support keyboard
• Fix for: Context menus are only openable with a mouse (no keyboard or mobile support)
• Fix for: Cell validation errors are only visible on hover (no keyboard or mobile support)
• Fix for: Cell navigation is not friendly with screen reader software
• Fix for: Fill up/down is only available with a mouse (no keyboard or mobile support)
• Fix for: can't move focus to the cell navigation menu with a key shortcut (discovered by @grantfitzsimmons)

Or, could simply implement #844 so that users can edit the datasets in Google Sheets instead