gRPC Trailers-Only responses must be a single HEADERS frame

[mgodave]

Replaces #3148

Motivation

When a blocking gRPC endpoint with streaming response encounters an exception, it attempts to send Trailers-Only response (grpc-status is returned in headers rather than trailers). However, the HTTP/2 layer sends two frames instead of one: HEADERS with endStream=false and DATA with endStream=true. Official grpc-java implementation doesn't like that, it wants a single HEADERS frame with endStream=true for Trailers-Only responses.

Changes

I added a filter and a context key to signal when we have a case where Trailers-Only response is sent. The filter will aggregate the response stream, observe there are no trailers, drop them, and will only return a single HEADERS frame with endStream=true.
This behavior can be tested by ProtocolCompatibilityTest.unimplementedServiceError, we unskipped tests that were failing before this fix.

Results

Before Change:

OUTBOUND HEADERS: streamId=3 headers=GrpcHttp2OutboundHeaders[:authority: 127.0.0.1:62451, :path: /grpc.netty.Compat/clientStreamingCall, :method: POST, :scheme: http, content-type: application/grpc, te: trailers, user-agent: grpc-java-netty/1.64.1, grpc-accept-encoding: gzip] streamDependency=0 weight=16 exclusive=false padding=0 endStream=false
OUTBOUND DATA: streamId=3 padding=0 endStream=false length=7 bytes=00000000020801
OUTBOUND DATA: streamId=3 padding=0 endStream=true length=0 bytes=
INBOUND HEADERS: streamId=3 headers=GrpcHttp2ResponseHeaders[:status: 200, server: servicetalk-grpc/, content-type: application/grpc+proto, grpc-status: 12, grpc-message: Method grpc.netty.Compat/clientStreamingCall is unimplemented] padding=0 endStream=false
INBOUND DATA: streamId=3 padding=0 endStream=true length=0 bytes=

After Change:

OUTBOUND HEADERS: streamId=3 headers=GrpcHttp2OutboundHeaders[:authority: 127.0.0.1:62421, :path: /grpc.netty.Compat/clientStreamingCall, :method: POST, :scheme: http, content-type: application/grpc, te: trailers, user-agent: grpc-java-netty/1.64.1, grpc-accept-encoding: gzip] streamDependency=0 weight=16 exclusive=false padding=0 endStream=false
OUTBOUND DATA: streamId=3 padding=0 endStream=false length=7 bytes=00000000020801
OUTBOUND DATA: streamId=3 padding=0 endStream=true length=0 bytes=
INBOUND HEADERS: streamId=3 headers=GrpcHttp2ResponseHeaders[:status: 200, server: servicetalk-grpc/, content-type: application/grpc+proto, grpc-status: 12, grpc-message: Method grpc.netty.Compat/clientStreamingCall is unimplemented, content-length: 0] padding=0 endStream=true

[idelpivnitskiy]

Glad that all tests passed 🎉

[idelpivnitskiy]

LGTM!
Will wait until my PR is merged and then will merge yours on Monday