* simplify extension communication proxy and add tests

* use async in jsonrpc2 connection tests

* add async result jsonrpc2 connection test

* remove unnecessary sendRequest signature

* be consistent about use of variadic params in jsonrpc2 connection library

* factor out send{Notification,Request}

* use Observable for jsonrpc2 sendRequest

* move handler types into connection.ts

* use AbortController/AbortSignal instead of custom CancellationToken

* actually implement canceling undispatched requests

* fix types for jsonrpc2 handlers

* add test for request abort

* use abortable-rx, still expose Promise API

* support Observables with a single emission

* support Observables with multiple emissions

* support proxying Observables

* extract isPromise

* add isSubscribable

* support language feature providers returning Observables with multiple emissions

NOCHANGELOG