test/evp_test.c: modify to use OSSL_PROVIDER_available()

test/evp_test.c: modify to use OSSL_PROVIDER_available()

This changes the stanza format used so far.  Some test stanza had the
following line, only possible for digests:

    Legacy = 1

These have been traded for the following:

    Availablein = legacy

That line is globally available in all test stanza and can be used to
tell what providers a certain algorithm may be available in.  Only one
provider needs to match, so one might have something like this for
some tests:

    Availablein = default fips

This means that one of those providers must be available for the test
stanza to be performed.

If the providers mentioned for a stanza aren't available, the test is
skipped.
If this line isn't used in a stanza, the algorithm is assumed to be
available unconditionally (either by fallback providers, or providers
loaded by the config file).

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/9398)