Select multiple countries

I have fixed this issues

Closing with a grovelling apology, because it appears everything is by design. However, during dev the js on our local machines does not correctly activate the ajax callback which transforms the select into a multi - and there were no errors to illustrate this. Similarly, on a separate dev instance on gitpod, the error checking failed to work altogether, which I have no explanation for.

So as it goes, this works fine. If you need multiple "countries" (this is contentious in my use case) this will in fact work fine, you just have to make sure it isn't something else that's making you look like an a$$! :|

Reopening because on further inspection, if we switch to E164 in order to accommodate multiple countries, we then have to use a different format for the data input, which isn't what we want. All the +44 'countries' have the same format, and we want to input them identically to how they are written locally, i.e. 07777123456.

Simple fix for this is to allow multiple selections whilst using the National option in the field config. This means changing the multiple to always be true, and less importantly removal of the now-unnecessary ajax callback etc.

@NikLP, I have created a new patch , please verify the attached patch