Fix false positives of IS_*() macros for 8-bit ASCII characters

Fixes #5778, #5840

The various IS_*() macros did not work correctly for 8-bit ASCII
characters with the high bit set, because the CVT(a) preprocessor
macro and'ed the given ASCII value with 0x7F, effectively folding
the high value range 128-255 over the low value range 0-127.
As a consequence, some of the IS_*() erroneously returned TRUE.

This commit fixes the issue by adding range checks instead of
cutting off high order bits using a mask. In order avoid multiple
evaluation of macro arguments, most of the implementation was moved
from macros into a static function is_keytype().

Thanks to Румен Петров for reporting and analyzing the UTF-8 parsing
issue #5840.

Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/5903)