[5.3] Changed startsWith and endsWith to use substr (non mbstring) (#…

…15380)

* Changed startsWith and endsWith to use substr (non mbstring), this is ok here because it doesn't
matter whether it's multi-byte unicode chars or not, just that the same number of bytes match at
the start or the end.

The performance of the existing methods becomes increasingly slow with larger strings due to
 mbstring functions.

* removed spacing between parenthesis

src/Illuminate/Support/Str.php

@@ -87,7 +87,7 @@ public static function contains($haystack, $needles)
     public static function endsWith($haystack, $needles)
     {
         foreach ((array) $needles as $needle) {
-            if ((string) $needle === static::substr($haystack, -static::length($needle))) {
+            if ((string) $needle === substr($haystack, - strlen($needle)))  {
                 return true;
             }
         }
@@ -403,7 +403,7 @@ public static function snake($value, $delimiter = '_')
     public static function startsWith($haystack, $needles)
     {
         foreach ((array) $needles as $needle) {
-            if ($needle != '' && mb_strpos($haystack, $needle) === 0) {
+            if ($needle != '' && substr($haystack, 0, strlen($needle)) === $needle) {
                 return true;
             }
         }