1315 - Add visually hidden <label> to combobox control.

[LukeLeber]

This changeset includes the following:

• Adds an id attribute to the combobox control
• Adds a <label> element that acts as the accessible name with the text Telephone country code
• Adds a style that visually hides the <label> element to preserve B/C

My only other concern is that the label text is not internationalized properly, but there are other instances of this as well. Bringing full i18n support to the project could likely happen in a follow-up. :slightly_smiling_face:

Thanks for your consideration!

Closes #1315

[mryand]

@jackocnr Can you provide any input on the status of this PR?

[jackocnr]

https://github.com/jackocnr/intl-tel-input/issues/1315#issuecomment-1497863987