[8.x] Add multibyte support to string padding helper functions (#41899)

* Add multibyte support to string padding helper functions

* Remove non-private `mbStrPad` method

* Fix code style

* Inline `str_pad` multibyte fix

Author: clarkewing

src/Illuminate/Support/Str.php

@@ -489,7 +489,7 @@ public static function matchAll($pattern, $subject)
      */
     public static function padBoth($value, $length, $pad = ' ')
     {
-        return str_pad($value, $length, $pad, STR_PAD_BOTH);
+        return str_pad($value, strlen($value) - mb_strlen($value) + $length, $pad, STR_PAD_BOTH);
     }
 
     /**
@@ -502,7 +502,7 @@ public static function padBoth($value, $length, $pad = ' ')
      */
     public static function padLeft($value, $length, $pad = ' ')
     {
-        return str_pad($value, $length, $pad, STR_PAD_LEFT);
+        return str_pad($value, strlen($value) - mb_strlen($value) + $length, $pad, STR_PAD_LEFT);
     }
 
     /**
@@ -515,7 +515,7 @@ public static function padLeft($value, $length, $pad = ' ')
      */
     public static function padRight($value, $length, $pad = ' ')
     {
-        return str_pad($value, $length, $pad, STR_PAD_RIGHT);
+        return str_pad($value, strlen($value) - mb_strlen($value) + $length, $pad, STR_PAD_RIGHT);
     }
 
     /**

tests/Support/SupportStrTest.php

@@ -609,18 +609,21 @@ public function testPadBoth()
     {
         $this->assertSame('__Alien___', Str::padBoth('Alien', 10, '_'));
         $this->assertSame('  Alien   ', Str::padBoth('Alien', 10));
+        $this->assertSame('  ❤MultiByte☆   ', Str::padBoth('❤MultiByte☆', 16));
     }
 
     public function testPadLeft()
     {
         $this->assertSame('-=-=-Alien', Str::padLeft('Alien', 10, '-='));
         $this->assertSame('     Alien', Str::padLeft('Alien', 10));
+        $this->assertSame('     ❤MultiByte☆', Str::padLeft('❤MultiByte☆', 16));
     }
 
     public function testPadRight()
     {
         $this->assertSame('Alien-----', Str::padRight('Alien', 10, '-'));
         $this->assertSame('Alien     ', Str::padRight('Alien', 10));
+        $this->assertSame('❤MultiByte☆     ', Str::padRight('❤MultiByte☆', 16));
     }
 
     public function testSwapKeywords(): void

tests/Support/SupportStringableTest.php

@@ -828,18 +828,21 @@ public function testPadBoth()
     {
         $this->assertSame('__Alien___', (string) $this->stringable('Alien')->padBoth(10, '_'));
         $this->assertSame('  Alien   ', (string) $this->stringable('Alien')->padBoth(10));
+        $this->assertSame('  ❤MultiByte☆   ', (string) $this->stringable('❤MultiByte☆')->padBoth(16));
     }
 
     public function testPadLeft()
     {
         $this->assertSame('-=-=-Alien', (string) $this->stringable('Alien')->padLeft(10, '-='));
         $this->assertSame('     Alien', (string) $this->stringable('Alien')->padLeft(10));
+        $this->assertSame('     ❤MultiByte☆', (string) $this->stringable('❤MultiByte☆')->padLeft(16));
     }
 
     public function testPadRight()
     {
         $this->assertSame('Alien-----', (string) $this->stringable('Alien')->padRight(10, '-'));
         $this->assertSame('Alien     ', (string) $this->stringable('Alien')->padRight(10));
+        $this->assertSame('❤MultiByte☆     ', (string) $this->stringable('❤MultiByte☆')->padRight(16));
     }
 
     public function testChunk()