Added a function to allocate a buffer and copy a maching param.
Added a function to allocate a buffer and concatenate all matching params.
Fixes#20717
Reviewed-by: Hugo Landau <hlandau@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/20724)
