internal/lsp/lsprpc: update binder tests to handle forwarding

Update the new binder tests to run both with a standalone server, and
with a forwarding chain.

Make a few superficial improvements along the way as well.

Change-Id: Icd197698093a3f6149ab58171806b2388ed75b7f
Reviewed-on: https://go-review.googlesource.com/c/tools/+/321134
Trust: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
gopls-CI: kokoro <noreply+kokoro@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Ian Cottrell <iancottrell@google.com>

internal/jsonrpc2/serve_test.go

@@ -89,7 +89,7 @@ func TestServe(t *testing.T) {
 			return jsonrpc2.NetListener(ctx, "tcp", "localhost:0", jsonrpc2.NetListenOptions{})
 		}},
 		{"pipe", func(ctx context.Context) (jsonrpc2.Listener, error) {
-			return jsonrpc2.NetPipe(ctx)
+			return jsonrpc2.NetPipeListener(ctx)
 		}},
 	}