CORE: Add the key object generator libcrypto<->provider interface

CORE: Add the key object generator libcrypto<->provider interface

We introduce these dispatched functions:

-   OP_keymgmt_gen_init() to initialize the key object generation.
-   OP_keymgmt_gen_set_template() to set a template for key object
    generation.  The template is another key object, for example one
    with domain parameters.
-   OP_keymgmt_gen_set_params() to set other key object generation
    parameters.
-   OP_keymgmt_gen_settable_params() to find out what settable
    parameters there are.
-   OP_keymgmt_gen() to perform the key object generation.
-   OP_keymgmt_gen_cleanup() to clean up the key object generation.

Internal function for easy and consistent use of these ddispatched
functions are added.

Reviewed-by: Shane Lontis <shane.lontis@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/10289)