Selects dropdowns should not be clipped by their container elements

[marcoambrosini]

When a user clicks on a select element and a dropdown is shown, the dropdown container should not be clipped by the boundaries of the parent container (this happens in NcActions and NcModal).

Initially discussed here nextcloud/notes#1242

how it is	what it looks like it should be

credits to @PowerUser64 for the mockup

cc @ShGKme & @susnux 🫶

[susnux]

Looks like the dropdown is mounted to the wrong container (should be body).

[nikhil2297]

When NcSelect is used inside NcActionInput (within NcActions) with :appendToBody="true", the dropdown menu appears behind the NcPopover container

Current Behavior	Expected Behavior

Solution :
Issue is with the z-index of NcSelect

cc @susnux