Make the iterator iterate over code points rather than characters

Also fix performance measurement for the iterator; it was all wrong.

lib/Encoding/UTF8.php

@@ -36,7 +36,7 @@ class UTF8 implements \Iterator {
     }
 
     public function current() {
-        return $this->current ?? ($this->current = $this->nextChar());
+        return $this->current ?? ($this->current = $this->nextCode());
     }
 
     public function key() {

perf/perf.php

@@ -35,13 +35,6 @@ $tests = [
             $c = $i->nextChar();
         }
     }],
-    'Native iterator' => ["", function(string $text) {
-        $c = null;
-        $i = new UTF8($text);
-        while ($c !== "") {
-            $c = $i->nextChar();
-        }
-    }],
     'Intl code points' => ["intl", function(string $text) {
         $i = (function($text) {
             $i = \IntlBreakIterator::createCodePointInstance();
@@ -61,6 +54,11 @@ $tests = [
             $p = $i->nextCode();
         }
     }],
+    'Code point iterator' => ["", function(string $text) {
+        $c = null;
+        $i = new UTF8($text);
+        foreach ($i as $c);
+    }],
 ];
 
 if (!file_exists(__DIR__."/docs/")) {

tests/cases/Encoding/TestUTF8.php

@@ -66,15 +66,12 @@ class TestUTF8 extends \PHPUnit\Framework\TestCase {
     */
     public function testIterateThroughAString(string $input, array $exp) {
         $out = [];
-        $exp = array_map(function ($v) {
-            return \IntlChar::chr($v);
-        }, $exp);
         $s = new UTF8($input);
         $a = 0;
         $this->assertTrue(true); // prevent risky test of empty string
-        foreach ($s as $index => $c) {
+        foreach ($s as $index => $p) {
             $this->assertSame($a, $index, "Character key at index $a reported incorrectly");
-            $this->assertSame(bin2hex($exp[$a]), bin2hex($c), "Character at index $a decoded incorrectly");
+            $this->assertSame($exp[$a], $p, "Character at index $a decoded incorrectly");
             $a++;
         }
     }