STORE: Move the built-in 'file:' loader to become an engine module

STORE: Move the built-in 'file:' loader to become an engine module

From this point on, this engine must be specifically specified.

To replace the internal EMBEDDED hack with something unique for the
new module, functions to create application specific OSSL_STORE_INFO
types were added.

Furthermore, the following function had to be exported:

ossl_do_blob_header()
ossl_do_PVK_header()
asn1_d2i_read_bio()

Finally, evp_pkcs82pkey_int() has become public under a new name,
EVP_PKCS82PKEY_with_libctx()

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/12587)