docs: Fix member index for mw.html

docs: Fix member index for mw.html

Method mw.html#element was indexed as being a member of
class mw.html.Cdata due to the lack of an explicit @member
tag, so it defaulted to linear association to the previous
@class block.

Quick fix can be done inline with @member but might as well
do it propert and separate the linear sequences.

Change-Id: I22580a6257a681a30e1ecd7c1283b57d7cb730f2