template options empty in Toc type form

Using TOC API for a new module (TOC API node) using it, I met some issue with the TOC Type form, not directly related with the module but with the theme used on a project.

Problem

Bootstrap theme, and any subthemes, add custom variables into the template settings (icon, icon_only, etc). And because the theme implementation do not match anymore the conditions in the TocTypeForm, the select list of templates is empty.

i.e. condition
array_keys($template_settings['variables']) == ['toc', 'attributes'])
is always FALSE

Proposition

Instead of checking if the array $template_settings['variables'] is exactly these two keys toc, attributes, just exclude the toc theme implementations that has the "item" key (and so toc_header and toc_back_to_top).

Another option would be to add a specific key to filter the toc theme implemntations

Patch follow