[Php74] Align mb_str_split() polyfill with Mbstring and native

The Php74 copy of mb_str_split() returned false for a length lower than 1
even on PHP 8+, where the function raises a ValueError, and used a single
.{N} quantifier that fails to compile for a length above the PCRE 65535
limit. Match the Mbstring implementation: throw ValueError on PHP 8+ and
chunk the regex so both polyfills behave identically.

Author: nicolas-grekas

src/Php74/Php74.php

@@ -50,17 +50,28 @@ public static function mb_str_split($string, $split_length = 1, $encoding = null
         }
 
         if (1 > $split_length = (int) $split_length) {
-            trigger_error('The length of each segment must be greater than zero', \E_USER_WARNING);
+            if (80000 > \PHP_VERSION_ID) {
+                trigger_error('The length of each segment must be greater than zero', \E_USER_WARNING);
 
-            return false;
+                return false;
+            }
+
+            throw new \ValueError('Argument #2 ($length) must be greater than 0');
         }
 
         if (null === $encoding) {
             $encoding = mb_internal_encoding();
         }
 
         if ('UTF-8' === $encoding || \in_array(strtoupper($encoding), ['UTF-8', 'UTF8'], true)) {
-            return preg_split("/(.{{$split_length}})/us", $string, -1, \PREG_SPLIT_DELIM_CAPTURE | \PREG_SPLIT_NO_EMPTY);
+            $rx = '/(';
+            while (65535 < $split_length) {
+                $rx .= '.{65535}';
+                $split_length -= 65535;
+            }
+            $rx .= '.{'.$split_length.'})/us';
+
+            return preg_split($rx, $string, -1, \PREG_SPLIT_DELIM_CAPTURE | \PREG_SPLIT_NO_EMPTY);
         }
 
         $result = [];

tests/Php74/Php74Test.php

@@ -12,6 +12,7 @@
 namespace Symfony\Polyfill\Tests\Php74;
 
 use PHPUnit\Framework\TestCase;
+use Symfony\Polyfill\Php74\Php74;
 
 /**
  * @author Ion Bazan <ion.bazan@gmail.com>
@@ -116,6 +117,27 @@ public function testStrSplitWithInvalidValues()
         $this->expectWarningMessage('The length of each segment must be greater than zero');
         mb_str_split('победа', 0);
     }
+
+    /**
+     * @covers \Symfony\Polyfill\Php74\Php74::mb_str_split
+     *
+     * @requires PHP 8
+     */
+    public function testStrSplitThrowsOnInvalidLength()
+    {
+        $this->expectException(\ValueError::class);
+        $this->expectExceptionMessage('Argument #2 ($length) must be greater than 0');
+
+        Php74::mb_str_split('победа', 0);
+    }
+
+    /**
+     * @covers \Symfony\Polyfill\Php74\Php74::mb_str_split
+     */
+    public function testStrSplitWithLengthAbovePcreLimit()
+    {
+        $this->assertSame([str_repeat('x', 70000)], Php74::mb_str_split(str_repeat('x', 70000), 70000, 'UTF-8'));
+    }
 }
 
 class A