Support at+jwt access token type

[ronnybremer]

php-jwt/src/Parser.php

Line 154 in 6555d0d

if ($fields['typ'] !== 'JWT') {

This code line will throw an exception when any other JTW type besides "jwt" is found.
This RFC https://datatracker.ietf.org/doc/html/rfc9068 registers the type "at+jwt" for OAuth2 access tokens and I think this library should be able to validate them.

Section 4 of the RFC outlines the validation steps needed, which seems to be pretty much in line with what this library does anyway:

• validate signature
• validate ISS
• validate AUD
• validate EXP

In case the access token is encrypted, it would need to be decrypted, same holds for type "jwt". What do you think?