crypto: key size must be int32 in DiffieHellman()

The JS code accepted any value where `typeof sizeOrKey === 'number'`
was true but the C++ code checked that `args[0]->IsInt32()` and
subsequently aborted.

Fixes: https://github.com/nodejs/node/issues/32738

PR-URL: https://github.com/nodejs/node/pull/32739


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Zeyu Yang <himself65@outlook.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>