Update international code as user types phone

[jmhooper]

Why: It is confusing that the international code selection and the
number in the phone input can be out of sync. This commit keeps both in
sync by updating them as the user types. This also helps make sure the
format of phone number makes a little more sense.

[zachmargolis]

typo: Internaional -- instead of Interna__t__ional

[jmhooper]

oops 😳

[monfresh]

I'm testing this locally and it's not doing what I think it should be doing.
For example:

• Select Morocco from the dropdown -> this automatically adds +212 in the text field. Then, when I start entering more digits, it's still formatting them as if it were a US number, i.e. it encloses the first 3 digits I type within parentheses, etc.
• If I enter as many digits as the text field will let me, which is one too many in the case of Morocco, when I submit the form, it tells me the number is invalid, but the text field now is no longer formatted, and the country code is duplicated. For example, if originally the text field was +212 (333) 333-3333, after submitting the form, it becomes +212 21 2333 3333333

[monfresh]

This line is missing a closing square bracket after the closing single quote. It's what's causing the tests to fail. Interestingly, Chrome doesn't complain about this, but Safari does.

[jmhooper]

Select Morocco from the dropdown -> this automatically adds +212 in the text field. Then, when I start entering more digits, it's still formatting them as if it were a US number, i.e. it encloses the first 3 digits I type within parentheses, etc.

I've pulled in libphonenumber-js and re-written the phone number formatter so it's a bit smarter about international numbers. There are some drawbacks. For example, it's significantly more complicated to figure out how to position the cursor when international numbers are in play. Some of the awkward behavior is on display in our other formatted fields though, and was on display in the old formatted phone field so I'm not too concerned about it.

If I enter as many digits as the text field will let me, which is one too many in the case of Morocco, when I submit the form, it tells me the number is invalid, but the text field now is no longer formatted, and the country code is duplicated. For example, if originally the text field was +212 (333) 333-3333, after submitting the form, it becomes +212 21 2333 3333333

This is not introduced by the changes in this PR. I plan on addressing that issue in #1571 since that will touch the form code where the bug lives.

I've also changed some of the JS to get this to work on the update user form phone.

Everything should be ready for another round of 👀s

[jmhooper]

Failing specs 🙃. Flipping back to WIP. Once sec

[jmhooper]

Specs are ✅. Now this is ready for another set of 👀s

[zachmargolis]

LGTM