[3.13] gh-123339: Fix cases of inconsistency of __module__ and __firstlineno__ in classes (GH-123613) (#124735)

* Setting the __module__ attribute for a class now removes the
  __firstlineno__ item from the type's dict.
* The _collections_abc and _pydecimal modules now completely replace the
  collections.abc and decimal modules after importing them. This
  allows to get the source of classes and functions defined in these
  modules.
* inspect.findsource() now checks whether the first line number for a
  class is out of bound.
(cherry picked from commit 69a4063ca5)

Lib/test/test_builtin.py

@@ -2564,6 +2564,7 @@ class TestType(unittest.TestCase):
         self.assertEqual(A.__module__, __name__)
         self.assertEqual(A.__bases__, (object,))
         self.assertIs(A.__base__, object)
+        self.assertNotIn('__firstlineno__', A.__dict__)
         x = A()
         self.assertIs(type(x), A)
         self.assertIs(x.__class__, A)
@@ -2642,6 +2643,17 @@ class TestType(unittest.TestCase):
             A.__qualname__ = b'B'
         self.assertEqual(A.__qualname__, 'D.E')
 
+    def test_type_firstlineno(self):
+        A = type('A', (), {'__firstlineno__': 42})
+        self.assertEqual(A.__name__, 'A')
+        self.assertEqual(A.__module__, __name__)
+        self.assertEqual(A.__dict__['__firstlineno__'], 42)
+        A.__module__ = 'testmodule'
+        self.assertEqual(A.__module__, 'testmodule')
+        self.assertNotIn('__firstlineno__', A.__dict__)
+        A.__firstlineno__ = 43
+        self.assertEqual(A.__dict__['__firstlineno__'], 43)
+
     def test_type_typeparams(self):
         class A[T]:
             pass