Add nghttp2_check_header_value_rfc9113 which verifies the additional
rule imposed by RFC 9113, section 8.2.1, that is a field value must
not start or end with 0x20(SPC) or 0x09(HTAB).
libnghttp2 uses this new function internally.
nghttp2 library itself now accept octet header/value pairs,
completely not restricted by HTTP/1 header name/value rule.
The applications may impose restriction about them using
validators.
Tatsuhiro Tsujikawa