UI: add a Custom Properties panel to the View Layer tab of properties.

Although view layers aren't ID, they do support custom properties,
so not providing the UI to access them seems to be a simple oversight.

release/scripts/startup/bl_ui/properties_view_layer.py

@@ -1,5 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0-or-later
-from bpy.types import Menu, Panel, UIList
+from bpy.types import Menu, Panel, UIList, ViewLayer
+
+from rna_prop_ui import PropertyPanel
 
 
 class VIEWLAYER_UL_aov(UIList):
@@ -249,6 +251,14 @@ class VIEWLAYER_PT_layer_passes_lightgroups(ViewLayerLightgroupsPanel):
     COMPAT_ENGINES = {'CYCLES'}
 
 
+class VIEWLAYER_PT_layer_custom_props(PropertyPanel, Panel):
+    bl_space_type = 'PROPERTIES'
+    bl_region_type = 'WINDOW'
+    bl_context = "view_layer"
+    _context_path = "view_layer"
+    _property_type = ViewLayer
+
+
 classes = (
     VIEWLAYER_MT_lightgroup_sync,
     VIEWLAYER_PT_layer,
@@ -260,6 +270,7 @@ classes = (
     VIEWLAYER_PT_layer_passes_cryptomatte,
     VIEWLAYER_PT_layer_passes_aov,
     VIEWLAYER_PT_layer_passes_lightgroups,
+    VIEWLAYER_PT_layer_custom_props,
     VIEWLAYER_UL_aov,
 )