Anim: Add operator to 'solo' the active bone collection

With armature layers it was possible to, with one click, show a single
layer and hide all the others. This is now possible with bone collections
as well.

For that I added a new operator `armature.bone_collection_solo_visibility`,
with a button next to the list of bone collections. The icon is
`SOLO_ON`, which is also used in the NLA.

scripts/startup/bl_operators/anim.py

@@ -506,10 +506,31 @@ class ARMATURE_OT_sync_bone_color_to_selected(Operator):
         return {'FINISHED'}
 
 
+class ARMATURE_OT_bone_collection_solo_visibility(Operator):
+    """Hide all other bone collections and show the active one"""
+    bl_idname = "armature.bone_collection_solo_visibility"
+    bl_label = "Solo Visibility"
+    bl_options = {'REGISTER', 'UNDO'}
+
+    name: StringProperty(name='Bone Collection')
+
+    @classmethod
+    def poll(cls, context):
+        return context.object and context.object.type == 'ARMATURE' and context.object.data
+
+    def execute(self, context):
+        arm = context.object.data
+        active_bcoll = arm.collections.active
+        for bcoll in arm.collections:
+            bcoll.is_visible = bcoll == active_bcoll
+        return {'FINISHED'}
+
+
 classes = (
     ANIM_OT_keying_set_export,
     NLA_OT_bake,
     ClearUselessActions,
     UpdateAnimatedTransformConstraint,
     ARMATURE_OT_sync_bone_color_to_selected,
+    ARMATURE_OT_bone_collection_solo_visibility,
 )

scripts/startup/bl_ui/properties_data_armature.py

@@ -135,6 +135,8 @@ class DATA_PT_bone_collections(ArmatureButtonsPanel, Panel):
             col.separator()
             col.operator("armature.collection_move", icon='TRIA_UP', text="").direction = 'UP'
             col.operator("armature.collection_move", icon='TRIA_DOWN', text="").direction = 'DOWN'
+            props = col.operator("armature.bone_collection_solo_visibility", text="", icon='SOLO_ON')
+            props.name = active_bcoll.name
 
         row = layout.row()