Fix BIO_printf formatting for negative numbers formatted with %e

Fix BIO_printf formatting for negative numbers formatted with %e

Some parts of the formatting code assumed that the input number is
positive.  This is fixed by working on its absolute value.

test/bioprinttest.c is amended to test the output of negative numbers
as well.

Fixes #26973

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/27478)

(cherry picked from commit fb555eb7a1d523e9df5584b44d16d0f72417bd19)