src: store key data in separate class

This separates key handles from the actual key data:

+-----------------+
| NativeKeyObject |
+-----------------+
        ^
     extends
        |
+-----------------+    +-----------------+    +---------------+
| KeyObject  (JS) | -> | KeyObjectHandle | -> | KeyObjectData |
+-----------------+    +-----------------+    +---------------+

PR-URL: https://github.com/nodejs/node/pull/33360


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>