Domains: Convert characters to basic Latin, when possible

The WHOIS specification does not define the required character set to be
used, but most WHOIS servers use just the basic Latin character set, so
that's what we enforce too. This change automagically converts other
characters to their basic Latin versions using the `deburr` method from
Lodash. So `ś` becomes `s`, `ą` -> `a`, etc.

Fixes #12559

client/my-sites/upgrades/checkout/domain-details-form.jsx

@@ -3,7 +3,15 @@
  */
 import React from 'react';
 import classNames from 'classnames';
-import { camelCase, head, kebabCase, map, omit, reduce } from 'lodash';
+import {
+	camelCase,
+	deburr,
+	head,
+	kebabCase,
+	map,
+	omit,
+	reduce,
+} from 'lodash';
 
 /**
  * Internal dependencies
@@ -73,7 +81,7 @@ export default React.createClass( {
 		const sanitizedFieldValues = Object.assign( {}, fieldValues );
 		this.fieldNames.forEach( ( fieldName ) => {
 			if ( typeof fieldValues[ fieldName ] === 'string' ) {
-				sanitizedFieldValues[ fieldName ] = fieldValues[ fieldName ].trim();
+				sanitizedFieldValues[ fieldName ] = deburr( fieldValues[ fieldName ].trim() );
 				if ( fieldName === 'postalCode' ) {
 					sanitizedFieldValues[ fieldName ] = sanitizedFieldValues[ fieldName ].toUpperCase();
 				}