Fix redundant dividers on search for labels

[HesterG]

Labels search dropdowns have redundant dividers when searching for labels

This PR adds data-divider-index and data-divider-group to dynamically toggle the visibility of dividers depending on filtered results. And slightly changed the logic for adding the divider if there are both Labels and OrgLabels exist.

After:

Untitled.mov

Locations of the dropdowns:

On sidebar of issue/pr, and on repo issue/pr list

[wxiaoguang]

At first glance, it's quite hacky. I guess it's not the right way.

[silverwind]

In the video, the extra dividers are still seen while typing, so yes I think the solution can't be right.

[silverwind]

BTW, I generally think we should rewrite these labels dropdown to a format similar to GitHub:

[wxiaoguang]

Actually, Fomantic UI does very well for "hiding dividers".

We only needs 2 lines:

  $dropdownLabelFilter.dropdown('setting', {'hideDividers': 'empty'});
  $dropdownLabelFilter.dropdown('refreshItems');

• Fix label list divider #25312

[HesterG]

Actually, Fomantic UI does very well for "hiding dividers".

We only needs 2 lines:

  $dropdownLabelFilter.dropdown('setting', {'hideDividers': 'empty'});
  $dropdownLabelFilter.dropdown('refreshItems');

• Fix label list divider #25312

That's great, I will close this.