This also fixes the case where `templateResult` does not return a
string, where it will fall back to jQuery to set the value of the
option. This allows for the `templateResult` function to return a
jQuery or DOM element that contains the templated data.
Just like with the translation methods, only strings returned from
`templateResult` will be escaped.
The old flag icons have been transferred from the old repository to
the documentation, for use in the templates. Unfortunately I cannot
find a license for them, but I suspect a license isn't actually
needed considering the state flags are public.
This closes https://github.com/select2/select2/issues/3005.
This closes https://github.com/select2/select2/issues/818.
