Disallow U+3000 as the last character of a reserved-body.

[bhaible]

In all places where a 'reserved-body' can occur:

• in a reserved-statement,
• after a reserved-annotation or private-use-annotation, in a literal-expression, variable-expression, or annotation-expression, it can be followed by whitespace ('s' nonterminal).

A syntax ambiguity exists, because - as reported in #721 and #725 - a U+3000 character can occur as the last character of a 'reserved-body' (via a 'reserved-char') and also as first character of whitespace ('s' nonterminal).

According to the principles explained in #725, it is not desired that a 'reserved-body' ends with a U+3000 character; rather, the U+3000 character is meant to be interpreted as part of the following whitespace.

Test cases (written with \u escapes, for legibility): For reserved-statement:
.regex /foo/\u3000\u3000{xyz}{{hello}}
For reserved-annotation:
{ % foo bar \u3000\u3000 }
For private-use-annotation:
{ & foo bar \u3000\u3000 @x }

This patch removes this ambiguity, by disallowing U+3000 as the last character of a 'reserved-body'.

It thus fixes #725 and the second part of #721.

Details:

• U+3000 gets removed from 'content-char' and 'reserved-char'.
• Whereas simple-start-char, text-char, quoted-char stay the same (since U+3000 is already part of 's').

[aphillips]

The appears to be an obvious oversight in the addition of U+3000 to whitespace.