bpo-40334: Produce better error messages on invalid targets (GH-20106)

The following error messages get produced:
- `cannot delete ...` for invalid `del` targets
- `... is an illegal 'for' target` for invalid targets in for
  statements
- `... is an illegal 'with' target` for invalid targets in
  with statements

Additionally, a few `cut`s were added in various places before the
invocation of the `invalid_*` rule, in order to speed things
up.

Co-authored-by: Pablo Galindo <Pablogsal@gmail.com>

Lib/test/test_exceptions.py

@@ -251,9 +251,9 @@ class ExceptionTests(unittest.TestCase):
         check('def f():\n  x, y: int', 2, 3)
         check('[*x for x in xs]', 1, 2)
         check('foo(x for x in range(10), 100)', 1, 5)
+        check('for 1 in []: pass', 1, 5)
         check('(yield i) = 2', 1, 2)
         check('def f(*):\n  pass', 1, 8)
-        check('for 1 in []: pass', 1, 7)
 
     @cpython_only
     def testSettingException(self):