Comply with the Node.js convention that asynchronous functions should never throw synchronous exceptions

[mmomtchev]

swig/Doc/Manual/Javascript.html

Line 1113 in 75d9adb

<p>The usual Node.js convention is that functions that return a <code>Promise</code> should never throw synchronously, because this forces the end user to catch eventual errors in two distrinct ways. Throwing a C++ exception in a wrapped function will automatically result in a rejected <code>Promise</code>.</p>

Currently an asynchronous wrapper will throw synchronously if it fails to parse the Javascript arguments.

It will still reject the asynchronous Promise if the underlying C/C++ method throws or if one of the check typemap fails.

This is in contrast to the usual Node.js convention that a function that returns a Promise should never throw as this forces the caller to implement two error-checking semantics.

Implementing this requires a complete overhaul of the overloading resolution and implementing typecheck typemaps which are still not supported in Javascript.