test/endecoder_legacy_test.c: new test for legacy comparison

test/endecoder_legacy_test.c: new test for legacy comparison

It checks that all of these functions have a corresponding
OSSL_ENCODER implementation, and that the output is the same:

- i2d_{TYPE}PrivateKey
- i2d_{TYPE}PublicKey
- i2d_{TYPE}params
- i2d_{TYPE}_PUBKEY
- PEM_write_bio_{TYPE}PrivateKey
- PEM_write_bio_{TYPE}PublicKey
- PEM_write_bio_{TYPE}Parameters
- PEM_write_bio_{TYPE}_PUBKEY

It also checks that all of these functions have a corresponding
OSSL_DECODER implementation, and that the decoding result matches:

- d2i_{TYPE}PrivateKey()
- d2i_{TYPE}PublicKey(),
- d2i_{TYPE}params(),
- d2i_{TYPE}_PUBKEY(),
- PEM_read_bio_{TYPE}PrivateKey()
- PEM_read_bio_{TYPE}PublicKey()
- PEM_read_bio_{TYPE}params()
- PEM_read_bio_{TYPE}_PUBKEY()

Reviewed-by: Paul Dale <paul.dale@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/13262)