Implement HPack static compression

[Tratcher]

Today Kestrel does not use any of the HPack compression features when serializing response headers. Static compression looks like the easiest place to start.

Design notes:

• The static table is here: https://tools.ietf.org/html/rfc7541#appendix-A
• Make an enum that maps to the static header names. Associate this with the known headers in the response header collection.
• Rather than passing in an enumeration of <string, string> to the encoder, come up with another structure that allows passing in either the enum values or the strings.
• Stretch: the :status pseudo header has 7 static entries that include common values. All of the other static header values are request headers (though shared code with HttpClient would want to take advantage of those).

Related work:

• Dynamic compression Implement HPack dynamic compression #4715
• Huffman encoding Use Huffman code in HPackEncoder #4742

[analogrelay]

Another HTTP/2 perf improvement to be driven by @aspnet/grpc