In any Action Slot selector, when there is no slot selected yet, replace
the 'Duplicate' and 'Unassign' buttons with a large 'New' button. This
is consistent with the ID selector, which does the same thing.
Care is taken to ensure this is only applied to the use case of
selecting Action Slots, in order to minimize the UI changes in Blender
4.4.
The only other use case of `template_search()` that I could find, is the
View Layer selector in the top-right corner of the window. However, even
without the "_is this an Action Slot selector_" guard, it would not show
these changes, as Blender guarantees there is always a view layer
assigned. Add-ons may still use `template_search()` in other ways,
though, so it's still good to keep this guard in place.
Pull Request: https://projects.blender.org/blender/blender/pulls/135443
a03077c22d