SwiftNIO HTTP/2 1.26.0

SemVer Minor

• Integrate the multiplexer into the NIOHTTPHandler (#377, #379, #380, #381, #382, #383, #384, #386)

SemVer Patch

• Avoid an allocation in the outbound frame buffer (#385)
• Replace estimatedFrameSize with flowControlledSize and only count DATA frames (#387, #388)

Other Changes

• Make soundness check aware of 2023 (#378)
• Add regression testing for docs and fix the issues. (#389)
• Add docker-compose file for Swift 5.9 (#390)