Checkboxes are not displayed if the configured livetable column is hidden or non-sortable

The code of this macro is adding the checkboxes only if it can identify the passed column in the headers of the livetable, even if it will not use that header in any other way (the value is actually fetched from the row's JSON).

The test it uses for checking if the column exists in the livetable headers is based on a weak test: it checks whether an anchor exists in the header of the livetable, the one here https://github.com/xwiki/xwiki-platform/blob/1fb87c33b52ca02dbb89bf3cf8e057690de134a2/xwiki-platform-core/xwiki-platform-flamingo/xwiki-platform-flamingo-skin/src/main/resources/flamingo/macros.vm#L1424 .
As the code says, that element is added only if the column is sortable.

Starting with XWiki 11.8 and this commit https://github.com/xwiki/xwiki-platform/commit/3ac4a1084bc3bb4b436dac3279989985d5ef875a , the hidden columns are not considered sortable anymore, regardless of the actual column settings (which is quite normal).