Improve webform support
- Make phone's composite elements available as webform tokens
- Consolidate webform's phone number settings into a single fieldset.
- Render field description because PhoneNumber form element expects it to be a string not a render array (originally reported in the issue #3059901)
- Make the default placeholder text translatable
- Simplify code for adding phone number properties to the form element
- Improve description of the webform phone_number element.
Closes #3036641