runtime(python): Highlight built-in constants in Python

Also add syntax tests for those newly constants.

closes: #17788
closes: #18922

Signed-off-by: Rob B <github@0x7e.net>
Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/syntax/testdir/input/python_constants_builtin_default.py

@@ -0,0 +1,11 @@
+# Built-in Constants
+# https://docs.python.org/3/library/constants.html
+
+# VIM_TEST_SETUP unlet g:python_constant_highlight
+# VIM_TEST_SETUP unlet g:python_no_builtin_highlight
+test = False
+test = True
+test = None
+test = NotImplemented
+test = Ellipsis
+test = __debug__