time: add some additional utilities and document everything
Some of the recently added functions were not documents. This has been addressed.
Also added utility functions for conversions between time_t, seconds and struct timeval
to/from OSSL_TIME.
Reviewed-by: Todd Short <todd.short@me.com> Reviewed-by: Richard Levitte <levitte@openssl.org> Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/19082)