avoid locale-dependent string comparisons

It doesn't seem appropriate to use locale dependent ordering to sort the
variants and extensions for normalization.  The result of normalization
should be consistent.

The Unicode CLDR specficiation is not specific about how these tags are
sorted, it just says that they should be in "alphabetical order".  They
only contain a-z (lower case) and 0-9, so for most locales alphabetical
order is the same as the code point order we are now using.

This commit removes a dependency on the ECMAScript internationalization
API.  This API is not available everywhere, particularly on embedded
devices like TVs where storage space for internationalization data is
limited.  This is important as bcp-47-normalize is now used by dash.js
which in turn is used by many HbbTV applications.

lib/index.js

@@ -29,8 +29,6 @@ import {likely} from './likely.js'
 
 const own = {}.hasOwnProperty
 
-const collator = new Intl.Collator()
-
 /**
  * @param {Schema} base
  * @param {Partial<Schema>} changes
@@ -159,7 +157,7 @@ export function bcp47Normalize(tag, options) {
   removeLikelySubtags(schema)
 
   // 5. Sort variants, and sort extensions on singleton.
-  schema.variants.sort(collator.compare)
+  schema.variants.sort()
   schema.extensions.sort(compareSingleton)
 
   // 6. Warn if fields (currently only regions) should be updated but have
@@ -323,5 +321,11 @@ function add(object, key, value) {
  * @returns {number}
  */
 function compareSingleton(left, right) {
-  return collator.compare(left.singleton, right.singleton)
+  if (left.singleton > right.singleton) {
+    return 1;
+  } else if (left.singleton < right.singleton) {
+    return -1;
+  } else {
+    return 0;
+  }
 }