UI: Move Collection Visibility popover from 3D View header into the Sidebar

It's more practical to use this from the Sidebar, and takes away one item from the crowded header.

See T63527

release/scripts/startup/bl_ui/space_view3d.py

@@ -257,13 +257,6 @@ class VIEW3D_HT_header(Header):
 
         layout.separator_spacer()
 
-        # Collection Visibility
-        layout.popover(
-            panel="VIEW3D_PT_collections",
-            icon='GROUP',
-            text="",
-        )
-
         # Viewport Settings
         layout.popover(
             panel="VIEW3D_PT_object_type_visibility",
@@ -4390,9 +4383,9 @@ class VIEW3D_PT_view3d_cursor(Panel):
 
 class VIEW3D_PT_collections(Panel):
     bl_space_type = 'VIEW_3D'
-    bl_region_type = 'HEADER'
+    bl_region_type = 'UI'
+    bl_category = "View"
     bl_label = "Collections Visibility"
-    bl_ui_units_x = 10
 
     def _draw_collection(self, layout, view_layer, collection, index):
         need_separator = index