Refactor OSSL_STORE_LOADER_do_all_provided() to behave like OSSL_STORE_LOADER_fetch()

Refactor OSSL_STORE_LOADER_do_all_provided() to behave like OSSL_STORE_LOADER_fetch()

This is refactored to use inner_loader_fetch() without any given name,
which is just there to ensure all decoder implementations are made
into methods, and then use ossl_method_store_do_all() to list them
all.

This also adds the internal ossl_store_loader_do_all_prefetched(),
which can be used if pre-fetching needs to be done separately from
listing all the decoder implementations, or if listing may happen
multiple times.

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/15604)