ACTION-1102: Confirm SHOULD statements in role mapping table.

- Modified IA2 and ATK/AT-SPI mapping of button/aria-pressed:
-- changed "SHOULD" to "expose as" a toggle button.

- Modified ATK/AT-SPI mapping of listbox when child of combobox:
-- changed "SHOULD" to "expose as ROLE_MENU".

- Modified ATK/AT-SPI mapping of option when child of listbox
exposed as ROLE_MENU:
-- changed "SHOULD" to "expose as MENU_ITEM".

- For alert and alertdialog, left as is the "SHOULD fire an
alert event".