Fix #146588: raise exception when attempting invalid idproperty renaming in Python

Each name has to be unique within a group, so when renaming an idproperty, one
has to make sure that the parent group does not contain duplicates afterwards.
This patch raises a `NameError` when setting the name to one that exists
already. Alternatively, one could delete the already-existing property, but that
seems unexpected and the user should rather do that explicitly.

This also adds a new unit test for this case.

Pull Request: https://projects.blender.org/blender/blender/pulls/146892

tests/python/bl_pyapi_idprop.py

@@ -203,6 +203,14 @@ class TestIdPropertyCreation(TestHelper, unittest.TestCase):
         with self.assertRaises(TypeError):
             self.id[self.key_id] = self
 
+    def test_rename(self):
+        self.id["foo"] = {"a": 1}
+        self.id["bar"] = {"b": 2}
+        self.id["foo"].name = "foo"
+        self.id["bar"].name = "bar"
+        with self.assertRaises(NameError):
+            self.id["foo"].name = "bar"
+
 
 class TestIdPropertyUIData(TestHelper, unittest.TestCase):
     # Default testing idprop key identifier.