hookspecs: add `plugin_name` parameter to the `pytest_plugin_registered` hook

We have a use case for this in the next commit.

The name can be obtained by using `manager.get_name(plugin)`, however
this is currently O(num plugins) in pluggy, which would be good to
avoid. Besides, it seems generally useful.

changelog/11825.improvement.rst

@@ -0,0 +1 @@
+The :hook:`pytest_plugin_registered` hook has a new ``plugin_name`` parameter containing the name by which ``plugin`` is registered.

src/_pytest/config/__init__.py

@@ -490,15 +490,19 @@ class PytestPluginManager(PluginManager):
                 )
             )
             return None
-        ret: Optional[str] = super().register(plugin, name)
-        if ret:
+        plugin_name = super().register(plugin, name)
+        if plugin_name is not None:
             self.hook.pytest_plugin_registered.call_historic(
-                kwargs=dict(plugin=plugin, manager=self)
+                kwargs=dict(
+                    plugin=plugin,
+                    plugin_name=plugin_name,
+                    manager=self,
+                )
             )
 
             if isinstance(plugin, types.ModuleType):
                 self.consider_module(plugin)
-        return ret
+        return plugin_name
 
     def getplugin(self, name: str):
         # Support deprecated naming because plugins (xdist e.g.) use it.

src/_pytest/hookspec.py

@@ -63,12 +63,15 @@ def pytest_addhooks(pluginmanager: "PytestPluginManager") -> None:
 
 @hookspec(historic=True)
 def pytest_plugin_registered(
-    plugin: "_PluggyPlugin", manager: "PytestPluginManager"
+    plugin: "_PluggyPlugin",
+    plugin_name: str,
+    manager: "PytestPluginManager",
 ) -> None:
     """A new pytest plugin got registered.
 
     :param plugin: The plugin module or instance.
-    :param manager: pytest plugin manager.
+    :param plugin_name: The name by which the plugin is registered.
+    :param manager: The pytest plugin manager.
 
     .. note::
         This hook is incompatible with hook wrappers.