Use NcSelect for NcActionInput type multiselect

[raimund-schluessler]

This replaces the deprecated NcMultiselect with the new NcSelect component for the NcActionInput component of type multiselect.

Although it got better (the dropdown wasn't visible at all before), Like before, there currently still is a z-index issue for the select dropdown. This is because the NcActions component has a z-index: 100000 and the select dropdown only got 9999. Fixing this is tricky at the moment, because the dropdown gets appended to body without a custom class that could be targeted, which means we can only set the z-index for all select dropdowns globally, which I don't know whether we want this. The proper solution would be to enhance NcSelect to allow to set a custom dropdown class, but that needs an upstream fix.

	Before	After
select closed
select open

I propose we go ahead despite the z-index issue, since it is already better than before.

Fixes 1/3 of #3743.

[susnux]

Does not change much on the functionality (still that z-index issues), but from the styling it now looks different.
Could we adjust the border color to match up with the other input types?

Same with the border radius, it looks rounder than the other input types, but this was even before so not related to this PR (it just catch my eye).

[raimund-schluessler]

Does not change much on the functionality (still that z-index issues), but from the styling it now looks different. Could we adjust the border color to match up with the other input types?

Same with the border radius, it looks rounder than the other input types, but this was even before so not related to this PR (it just catch my eye).

I would say, the other inputs need to be adjusted. Ideally, we should use an NcTextField here, then the borders and their radii should look the same. I would rather not touch the NcSelect styling, though. I can do that in a follow-up PR later.
The z-index problem is annoying, but it still works, since the actions menu simply shows a scrollbar and you can still select the options.

[Pytal]

🎨

[nickvergessen]

Added a doc sample with object support: