header sorting is not work in HTML Column.

e.g.

columns: [
 { title: `<div>ONE</div><div>TWO</div>` }
],
stripHTML: false,

When doubleclick on header, e.target is div element.
it has not "data-x" attribute.

I think that should be get td element in getElement or new method.

I am concerned about the overlap between custom HTML headers and sort markers, but I think this should be handled by the user.
Currently, there is still overlap in very small columns.

I am also concerned that HTML cannot be used in Nested Header.

--
sorry, i'm not good at english.

Start by reproducing the reported double-click sorting case with an HTML header containing nested div elements and stripHTML set to false. Trace the header sorting path around getElement and verify that sorting works when the event target is a nested div rather than the table cell, while preserving the stated concerns about sort-marker overlap and nested headers.