Restructure the write code

Restructure the write code

Move the multiblock code into a separate file and introduce the usage of
record_functions_st for some write functions.

Reviewed-by: Hugo Landau <hlandau@openssl.org>
Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/19198)