Also `\U` after control/meta is invalid [Bug #17861]

	As well as `\u`, `\U` should be invalid there too.
	And highlight including `u`/`U` not only the backslash before it.
	---
	 parse.y                 | 12 ++++++++++--
	 test/ruby/test_parse.rb | 15 +++++++++++++++
	 2 files changed, 25 insertions(+), 2 deletions(-)