Remove dynamic setup of pytest.collect fake module

Make it a real module instead.

This was initially added in 9b58d6e
(pytest-dev#2315), when removing support
for `pytest_namespace`.

Not sure if it ever worked "properly", but currently
`import pytest.collect` and `from pytest.collect import File` do not
work (but with this patch).

This is only relevant for (backward) compatibility, but the more it
appears to make sense to move it into a lazily loaded, separate file.

src/_pytest/compat.py

@@ -336,30 +336,6 @@ def safe_isclass(obj: object) -> bool:
         return False
 
 
-COLLECT_FAKEMODULE_ATTRIBUTES = (
-    "Collector",
-    "Module",
-    "Function",
-    "Instance",
-    "Session",
-    "Item",
-    "Class",
-    "File",
-    "_fillfuncargs",
-)
-
-
-def _setup_collect_fakemodule() -> None:
-    from types import ModuleType
-    import pytest
-
-    # Types ignored because the module is created dynamically.
-    pytest.collect = ModuleType("pytest.collect")  # type: ignore
-    pytest.collect.__all__ = []  # type: ignore  # used for setns
-    for attr_name in COLLECT_FAKEMODULE_ATTRIBUTES:
-        setattr(pytest.collect, attr_name, getattr(pytest, attr_name))  # type: ignore
-
-
 class CaptureIO(io.TextIOWrapper):
     def __init__(self) -> None:
         super().__init__(io.BytesIO(), encoding="UTF-8", newline="", write_through=True)

src/pytest/__init__.py

@@ -3,7 +3,6 @@
 """
 from _pytest import __version__
 from _pytest.assertion import register_assert_rewrite
-from _pytest.compat import _setup_collect_fakemodule
 from _pytest.config import cmdline
 from _pytest.config import ExitCode
 from _pytest.config import hookimpl
@@ -90,7 +89,3 @@
     "xfail",
     "yield_fixture",
 ]
-
-
-_setup_collect_fakemodule()
-del _setup_collect_fakemodule

src/pytest/collect.py

@@ -0,0 +1,10 @@
+"""Fake module for backward compatibility."""
+from . import _fillfuncargs  # noqa: F401
+from . import Class  # noqa: F401
+from . import Collector  # noqa: F401
+from . import File  # noqa: F401
+from . import Function  # noqa: F401
+from . import Instance  # noqa: F401
+from . import Item  # noqa: F401
+from . import Module  # noqa: F401
+from . import Session  # noqa: F401