1. Show shortcuts for easy navigation.

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/27262

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/30149

Use more semantic `<button>` element and prevent the form from
submitting.

Make Sort dropdown behave the same as filters in narrower
viewports. Adjust dropdowns to fit on the same line in worst-case
scenario ("Oldest created" selected).

Closes #22562

See merge request !9533

Fixed the position of the loading spinner in the issue template dropdown
toggle. It was previously just positioned with the content, this now
correctly places it in the same place the chevron down is

Closes #28906

This ports some code over from EE to reduce conflicts

Signed-off-by: David Wagner <david@marvid.fr>

The chevron now has the same darker shade when the dropdown is opened it
had when hovered on.
Signed-off-by: David Wagner <david@marvid.fr>

Make sort and filter dropdowns look the same and tweak their icon and
colors according to #24150.
Signed-off-by: David Wagner <david@marvid.fr>