ch.exe's global states (e.g. sourceContext, module*Map) need to change to work cross-thread

WScriptJsrt uses global states to store sourceContext and maps for moduleRecords, etc..
Changes must be made to support cross-thread scenarios:

1) Module-related maps must be per JsContext to provide isolation between threads
2) Module-related maps have the same lifetime as JsContext
3) Code that updates sourceContext must be locked with critical sections