qapi/parser: don't parse rST markup as section headers

qapi/parser: don't parse rST markup as section headers

The double-colon synax is rST formatting that precedes a literal code
block. We do not want to capture these as QAPI-specific sections.

Coerce blocks that start with e.g. "Example::" to be parsed as untagged
paragraphs instead of special tagged sections.

Signed-off-by: John Snow <jsnow@redhat.com>
Message-ID: <20240626222128.406106-14-jsnow@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
[Indentation tweaked for consistency]
Signed-off-by: Markus Armbruster <armbru@redhat.com>