style(Reverse): add use statements

Author: azdanov

exercises/Reverse/Complete/ReverseComplete.php

@@ -4,9 +4,14 @@
 
 namespace Exercises\Reverse\Complete;
 
+use function abs;
 use function array_reduce;
 use function array_reverse;
 use function implode;
+use function log10;
+use function mb_strlen;
+use function mb_substr;
+use function pow;
 use function str_split;
 use function strlen;
 use function strrev;