[css-syntax] Revert (parts of) "Revert <unicode-range> changes from CSS 2.1"

This reverts parts of commit 2359070.

Namely:

* The tokens have a pair of integers, rather than strings or "a range".
* Keep the "Consume a unicode-range token" section as in earlier EDs.
* Remove the "Set the unicode-range’s range" section: the tokenizer does
no error handling / normalization beyond parsing hex digits into
integers.

Author: SimonSapin

css-syntax/Diagrams.src.html

@@ -153,10 +153,15 @@ <h3>Parsing</h3>
 		'U',
 		'u'),
 	'+',
-	Sequence(OneOrMore(Choice(0, NonTerminal('hex digit'), '?'), Comment('1-6 times'))),
-	Optional(Sequence(
-		'-',
-		OneOrMore(NonTerminal('hex digit'), Comment('1-6 times'))))));
+	Choice(0,
+		Sequence(OneOrMore(NonTerminal('hex digit'), Comment('1-6 times'))),
+		Sequence(
+			ZeroOrMore(NonTerminal('hex digit'), Comment('1-5 times')),
+			OneOrMore('?', Comment('1 to (6 - digits) times'))),
+		Sequence(
+			OneOrMore(NonTerminal('hex digit'), Comment('1-6 times')),
+			'-',
+			OneOrMore(NonTerminal('hex digit'), Comment('1-6 times'))))));
 
 add('〈include-match〉', Diagram('~='));