PY-30827 PyRenameElementQuickFix changed to avoid special handling of unit test cases

Test data and PyQuickFixTest are updated accordingly. Test for renaming in language injection added.

python/testData/inspections/RenameFunctionShadowingBuiltins_after.py

@@ -1,6 +1,6 @@
-def a(x):
+def A_NEW_NAME(x):
     return x
 
 
 def f():
-    return a('foo')
+    return A_NEW_NAME('foo')

python/testData/inspections/RenameShadowingBuiltins_after.py

@@ -1,3 +1,3 @@
 def f(name):
-    a = open(name, 'rb')
-    return a.read()
+    A_NEW_NAME = open(name, 'rb')
+    return A_NEW_NAME.read()