Improve accessibility - associate label and fields

[braders]

Overview

The primary purpose of this change was to associate the labels on the event location form with the relevant inputs:

As part of this change, I have also updated the contact forms so that the "ext" text becomes a label for the relevant telephone extension fields.

Before

The labels "Email 1:", "Phone 1:", "Ext" did not have a for attribute, and so were not associated with the input elements. This wasn't the end of the world as there is aria-label attributes in place, but adding the associations improves consistency, and means that mouse users can click on the labels to focus the relevant fields.

After

The labels have for attributes and so are semantically linked with the relevant fields.

Technical Details

I did consider just adding a hardcoded for attribute to the elements within the templates. However this seemed more brittle than using the style {$form.email.1.email.label}. This does mean that CRM_Contact_Form_Edit_Email::buildQuickForm and CRM_Contact_Form_Edit_Phone::buildQuickForm now set labels which may not be relevant to all scenarios where these methods are used. However I considered this ok, and any other contexts will simply ignore the labels unless they are explicitely rendered.

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[eileenmcnaughton]

I tried this out on the demo sites & it seems to work fine. I haven't been terribly involved in the accessibility work so gave it merge ready rather than merging in case anyone else wants to weigh in.

[yashodha]

@braders @eileenmcnaughton looks good, merging this.

[eileenmcnaughton]

thanks @yashodha