Add regression tests of instance attribute inference on builtins.object

Ref #3595, #4221, #3970, pylint-dev/astroid#945. Depends pylint-dev/astroid#946.

tests/functional/r/regression/regression_3595_notcallable_collections.py

@@ -0,0 +1,13 @@
+# pylint: disable=missing-docstring,unused-import
+# https://github.com/PyCQA/pylint/issues/3595
+
+import collections
+
+class Example:
+    def __init__(self):
+        self.prev()
+        self.next()
+    def prev(self):
+        pass
+    def next(self):
+        pass

tests/functional/r/regression/regression_4221_object_instanceattr.py

@@ -0,0 +1,8 @@
+# pylint: disable=missing-docstring
+# https://github.com/PyCQA/pylint/issues/4221
+
+import random
+o = object()
+if random.choice([True, False]):
+    o.count = None
+"abc".count("a")