Integrate pytest-faulthandler into the core

* Add pytest-faulthandler files unchanged
* Adapt imports and tests
* Add code to skip registration of the external `pytest_faulthandler`
  to avoid conflicts

Fix #5440

src/_pytest/config/__init__.py

@@ -141,6 +141,7 @@ default_plugins = essential_plugins + (
     "warnings",
     "logging",
     "reports",
+    "faulthandler",
 )
 
 builtin_plugins = set(default_plugins)
@@ -299,7 +300,7 @@ class PytestPluginManager(PluginManager):
         return opts
 
     def register(self, plugin, name=None):
-        if name in ["pytest_catchlog", "pytest_capturelog"]:
+        if name in _pytest.deprecated.DEPRECATED_EXTERNAL_PLUGINS:
             warnings.warn(
                 PytestConfigWarning(
                     "{} plugin has been merged into the core, "