Daemon Mode - Test/fix changing current directory when multiple requests come in simultaneously

[MikeBauerCA]

Test and fix changing current directory (and process environment) when multiple requests come in simultaneously.

[t1m0thyj]

Resolved in #1317 and #1322. Interleaved requests are now queued (see #1178 (comment)). This should eliminate any race conditions related to accessing current directory and environment variables in command handlers. Additionally, we stopped recommending use of process.stdin (use IHandlerParameters.stdin instead) since it only supports a one-time read operation. If we decide to support multithreaded concurrent requests in the future, we will need to revisit how we handle these things.