CORE: Encure that cached fetches can be done per provider

CORE: Encure that cached fetches can be done per provider

This mostly entails passing around a provider pointer, and handling
queries that includes a pointer to a provider, where NULL means "any".

This also means that there's a need to pass the provider pointer, not
just down to the cache functions, but also be able to get it from
ossl_method_store_fetch().  To this end, that function's OSSL_PROVIDER
pointer argument is modified to be a pointer reference, so the
function can answer back what provider the method comes from.

Test added.

Fixes #16614

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/16725)