Inconsistence of baggage value restriction

[leizhag]

Description

Member.String() accpets UTF-8 strings as baggage member values, and URL-encodes them. But it seems this URL-encoding has no effect since baggage.NewMember() does not accept UTF-8 strings.

Environment

• opentelemetry-go version: 1.9.0

Steps To Reproduce

1. baggage.NewMember("", ";") returns an error.

Expected behavior

baggage.NewMember("", ";") does not return errors or Member.String() does no URL-encoding.

[MrAlias]

baggage.NewMember("", ";") contains an invalid key: https://go.dev/play/p/Xeoi2wArkIn

It also contains an invalid value according to the W3C baggage specification: https://go.dev/play/p/oGeHN3Y52wl

The error returned from NewMember is valid based on how that function is defined:

// NewMember returns a new Member from the passed arguments. An error is
// returned if the created Member would be invalid according to the W3C
// Baggage specification.

As for underlying issue, the accepted value of NewMember is not decoded as the specification has added:

A value contains a string whose character encoding MUST be UTF-8 [Encoding]. Any characters outside of the baggage-octet range of characters MUST be percent-encoded. Characters which are not required to be percent-encoded MAY be percent-encoded. Percent-encoding is defined in [RFC3986], Section 2.1: https://datatracker.ietf.org/doc/html/rfc3986#section-2.1.

When decoding the value, percent-encoded octet sequences that do not match the UTF-8 encoding scheme MUST be replaced with the replacement character (U+FFFD).

baggage.NewMember("key", "%3B") should be interpreted with a value of ;. Instead it is interpreted directly: https://go.dev/play/p/16d_eij-CWt

The value accepted by NewMember needs to be decoded.

[NewReStarter]

@MrAlias hey, can i take this bug?