Enhanced integer parsing in OSSL_PARAM_allocate_from_text

Enhanced integer parsing in OSSL_PARAM_allocate_from_text

Fixes #14041 and additional bugs discovered by the newly created
tests.

This patch:
 - Introduces support for 0x prefixed integers
 - Fixes parsing of negative integers (negative numbers were
   shifted by -2)
 - Fixes ability to parse maximal unsigned numbers ("too small
   buffer" error used to be reported incorrectly)
 - Fixes a memory leak when OSSL_PARAM_allocate_from_text fails
   leaving a temporary BN allocated

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/14093)