Add error.cause property to errors which originate from an underlying host error

[JakeChampion]

For example, a fetch request may fail for a number of reasons, we can surface our own generic reason as well as the underlying reason if we use error.cause

js-compute-runtime/runtime/js-compute-runtime/core/event_loop.cpp

Line 149 in d4a4538

JS_ReportErrorUTF8(cx, "NetworkError when attempting to fetch resource.");