http2: refactor settings handling

Add `Http2Seettings` utility class for handling settings
logic and reducing code duplication.

PR-URL: https://github.com/nodejs/node/pull/16668


Reviewed-By: Sebastiaan Deckers <sebdeckers83@gmail.com>
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>
Reviewed-By: Khaidi Chu <i@2333.moe>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>