HttpClient.Version should provide an enum value for HTTP/3

A DESCRIPTION OF THE PROBLEM :
Even though the HTTP/3 protocol definition is still work in progress, there are already early implementations of the (draft) protocol. Because the HttpClient.Version enum only defines the values HTTP_1_1 and HTTP_2, Java implementations of HTTP/3 (see for example )https://bitbucket.org/pjtr/flupke/src/master/readme.md) cannot properly implement java.net.http.HttpClient, because of its version method.

The enum should be extended with a value for HTTP_3.