NIOHTTP2ServerConnectionManagementHandler doesn't handle input closed event

I'm looking into replacing the Hummingbird `HTTP2ServerConnectionManager` with the one that has been added to `swift-no-http2`. Both of them are based off the gRPC version so I thought I might be able to swap one out for the other. Unfortunately this isn't the case. It appears the NIO version does not handle inputClosed events and will leave the HTTP2 channel dangling, if a client closes the connection. Is it expected that these will be handled elsewhere?

Start by locating NIOHTTP2ServerConnectionManagementHandler and tracing how an inputClosed event is propagated when an HTTP/2 client closes its connection. Reproduce the client-close case and verify that the channel is no longer left dangling; the issue does not name a specific test or file.

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