fix: oc-drop a11y and overflow issues

[JammingBen]

Fixes 2 overflow issues with the OcDrop component:

• sub menus (e.g. "Open with...") now open to the left or right instead of to the bottom so other elements of the drop don't get covered
• the expanded select input in the view options drop now correctly overflows the drop so all items are accessible

Fixes a11y issues with the OcDrop component:

• drop menus are now properly navigable via arrow keys instead of tabs (with some exceptions where the drops are not classic menus, e.g. contextual helpers)
• drop menus and their items now have proper role attributes

fixes #2097
fixes #2081