Pose library: remove much of old pose library interface

Remove much of the old legacy pose library:
- Remove from the Pose & Armature menus.
- Remove from the default keymap.
- Pose Library panel in Armature properties: Add "(legacy)" to title.
- Add note that the functionality of that panel is obsolete, with a
  button that opens the manual on the chapter of the new pose library.
- Add button to convert the selected legacy pose library to pose assets.
- The rest of the functionality is greyed out to further communicate
  it's been deprecated. It's still functional, though.

Ref: T93405

release/scripts/startup/bl_ui/properties_data_armature.py

@@ -157,30 +157,53 @@ class DATA_PT_bone_groups(ArmatureButtonsPanel, Panel):
 
 
 class DATA_PT_pose_library(ArmatureButtonsPanel, Panel):
-    bl_label = "Pose Library"
+    bl_label = "Pose Library (Legacy)"
     bl_options = {'DEFAULT_CLOSED'}
 
     @classmethod
     def poll(cls, context):
         return (context.object and context.object.type == 'ARMATURE' and context.object.pose)
 
+    @staticmethod
+    def get_manual_url():
+        url_fmt = "https://docs.blender.org/manual/en/%d.%d/animation/armatures/posing/editing/pose_library.html"
+        return url_fmt % bpy.app.version[:2]
+
     def draw(self, context):
         layout = self.layout
 
+        col = layout.column(align=True)
+        col.label(text="This panel is a remainder of the old pose library,")
+        col.label(text="which was replaced by the Asset Browser.")
+
+        url = self.get_manual_url()
+        col.operator('wm.url_open', text="More Info", icon="WORLD").url = url
+
+        layout.separator()
+
         ob = context.object
         poselib = ob.pose_library
 
-        layout.template_ID(ob, "pose_library", new="poselib.new", unlink="poselib.unlink")
+        col = layout.column(align=True)
+        col.template_ID(ob, "pose_library", new="poselib.new", unlink="poselib.unlink")
 
         if poselib:
+            col.operator('poselib.convert_old_object_poselib',
+                text="Convert to Pose Assets", icon="ASSET_MANAGER")
+
+            # Put the deprecated stuff in its own sub-layout.
+
+            dep_layout = layout.column()
+            dep_layout.active = False
+
             # warning about poselib being in an invalid state
             if poselib.fcurves and not poselib.pose_markers:
-                layout.label(icon='ERROR', text="Error: Potentially corrupt library, run 'Sanitize' operator to fix")
+                dep_layout.label(icon='ERROR', text="Error: Potentially corrupt library, run 'Sanitize' operator to fix")
 
             # list of poses in pose library
-            row = layout.row()
+            row = dep_layout.row()
             row.template_list("UI_UL_list", "pose_markers", poselib, "pose_markers",
-                              poselib.pose_markers, "active_index", rows=5)
+                              poselib.pose_markers, "active_index", rows=3)
 
             # column of operators for active pose
             # - goes beside list