vale: check the whole \li entry in Qt.Structure.ListItemPunctuation

The rule matched a comma and conjunction at the end of the \li line, so
it warned on an entry that wraps after a line ending in "new name, and"
and finishes the sentence on the next line.

QDoc continues a list item until the next \li, \endlist, a blank line,
or a block command such as \code or \image. Vale's QDoc converter
already places those boundaries, so scope the rule to text & doc(li, td)
and anchor the pattern to the end of the entry with \z. A \li in a
\table becomes a td element, which doc(li, td) covers.

Add tests for wrapped entries, a continuation line starting with an
inline command or a macro, a conjunction on its own line, code inside
an entry, table cells, and entries that end before \note, \code, or a
blank line.

Change-Id: I9725723e76704b667b50372f8e87df0027327925
Reviewed-by: Venugopal Shivashankar <Venugopal.Shivashankar@qt.io>