First and foremost, this patch implements the latest best practices in C++ (i.e. comparison operators are not member functions).
The main objective of this rewrite is to have these operators callable in slightly more general contexts (*this->asFontTag() == *rhs.asFontTag() yielded an error because no member function could be called). This feature is no more required.
The rewrite took place in the context of https://www.lyx.org/trac/ticket/12585. The first iteration was using more complex code to circumvent XMLStream in DocBook (see details in the bug above and in the mailing list), while this one uses XMLStream fully. The bug was due to font tags being considered equal when they were not, due to the comparison done only on the XML tag and not on the actual font change (XML attributes can complement the tag for various font changes).
The new parameter allows more flexibility when encoding some elements that have a poor mapping in DocBook, like theorems. The major use is to wrap the environment in a generic container, figure, which requires a title (but none is available).
Useless parentheses (not helping with readability either) and semicolon. Redo indentation to be consistent throughout the file. Also, fix typos along the way.
* disambiguate "Other" label
* Add accelerator
* Add tooltip to "Other" widget
* Amend tooltip of "Web" widget (since "other" now seems to have taken
part of its function)
Missing return in `specialCharKindToXMLEntity`. Previously, the
functions that were merged into `specialCharKindToXMLEntity` did not
return any kind of error in case an unknown special character is met
(enumerated value). This behaviour is preserved.
This is a new take on c8e2c17a that was reverted at da67bde61a due to entities no more recognised by the browsers. Corresponding thread on the mailing list: https://www.mail-archive.com/lyx-devel@lists.lyx.org/msg213179.html
This patch is a huge cleanup overall, by removing the distinction between HTML and XML entities (the latter arrived due to the DocBook support).
In InsetListingParams, I also changed the mechanism that relied on " to use an XML entity to be consistent with the rest of the code, mostly in case someone looks for HTML entities and wonders why they are still there.
