Codemod the HSL to have coeffects

Summary:
`phps ConvertAttributesToCoeffectsCodemod` (but only on the HSL)

Then deal with the TParam arity issues. Either remove the explicit list if they add nothing or add a `_` to them

Reviewed By: rodmk

Differential Revision: D25806372

fbshipit-source-id: 7d1cf0cb6ec0ab4c95e67bb1f2a54aea49bf5293

Author: DavidSnider

src/os/ErrnoException.php

@@ -70,7 +70,7 @@ final public function getErrno(): Errno{
    * stays happy.
    */
   <<__Deprecated("Use `getErrno()` instead", 0), __Pure, __MaybeMutable>>
-  final public function getCode(): Errno {
+  final public function getCode()[]: Errno {
     return $this->errno;
   }
 }