[docblocks] Add MergePhpstanDocTagIntoNativeRector to merge @phpstan-* doc tags into native tags

[TomasVotruba]

Adds MergePhpstanDocTagIntoNativeRector that promotes the more precise @phpstan-var / @phpstan-param / @phpstan-return docblock tag into its native @var / @param / @return counterpart, dropping the weaker native duplicate.

 final class SomeClass
 {
     /**
-     * @var Collection
-     *
-     * @phpstan-var Collection<int, string>
+     * @var Collection<int, string>
      */
     private $items;
 }

Also handles method @param / @return:

     /**
-     * @param array $values
-     * @phpstan-param array<int, string> $values
-     *
-     * @return array
-     * @phpstan-return array<int, string>
+     * @param array<int, string> $values
+     *
+     * @return array<int, string>
      */
     public function process($values)

A @phpstan-* tag with no native counterpart is still renamed to native. Params are matched by name, so unrelated @param tags stay untouched.