PyDoc: Fix typing issues with bpy.utils.register_tool

- Add `type[]` for the `tool_cls` as it's expecting tool type class,
  not the instance (similar to #132420)
- Add `set[str]` to `after` type as it's seems to be the way it's used
  the most widely, e.g. in "UI Tool Simple" example that comes with Blender:

`bpy.utils.register_tool(MyTool, after={"builtin.scale_cage"}, separator=True, group=True)`

Pull Request: https://projects.blender.org/blender/blender/pulls/133975

scripts/modules/bpy/utils/__init__.py

@@ -1022,9 +1022,9 @@ def register_tool(tool_cls, *, after=None, separator=False, group=False):
     Register a tool in the toolbar.
 
     :arg tool_cls: A tool subclass.
-    :type tool_cls: :class:`bpy.types.WorkSpaceTool`
+    :type tool_cls: type[:class:`bpy.types.WorkSpaceTool`]
     :arg after: Optional identifiers this tool will be added after.
-    :type after: Sequence[str] | None
+    :type after: Sequence[str] | set[str] | None
     :arg separator: When true, add a separator before this tool.
     :type separator: bool
     :arg group: When true, add a new nested group of tools.