When using the commenting features (ex. toggle line commentation),
detect the the type of comments for the filetype of the line with
the caret rather than using the filetype of the current document.

Filetype is determined by the Scintilla state/style at the
beginning of the line where the caret is.

This does not fix the existing bug where using the commenting
features on lines with things like `<script>` will result in an
HTML-style comment to be wrapped around it and also where using
the commenting feature on a line with something like `<?php`
will not only wrap it in an HTML-style comment but it also won't
be able to uncomment the line.

This closes bug ID 2863829[1] and 3127598[2].

[1] https://sourceforge.net/tracker/?func=detail&aid=2863829&group_id=153444&atid=787791
[2] https://sourceforge.net/tracker/?func=detail&aid=3127598&group_id=153444&atid=787791