Further decoder tuning possibly better perf

Further decoder tuning possibly better perf

- The decoder should consider fewer options based on
  more precise tracking of the desired input type
  (DER, PVK, MSBLOB), algorithm (RSA, EC, ...),
  input structure (SPKI, P8, ...).

How much this affects actual use-cases is harder to estimate, we'll just
have to run before/after perf tests.

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Tim Hudson <tjh@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/26927)