Refactor: libcrmcommon: New pcmk__html_create()

This function doesn't set text content, even though every caller needs
to set text content on the resulting node. The caller must set text
content separately.

This decision was made for readability -- too many positional arguments
were deemed confusing.

https://github.com/ClusterLabs/pacemaker/pull/3386#discussion_r1516997973

Signed-off-by: Reid Wahl <nrwahl@protonmail.com>