Fixes and improvements for proxy and reflect

[duonglaiquang]

This PR does the following

Fix multiple issues in NativeProxy and NativeReflect.

1. NativeProxy: fix set trap not passing receiver object

put(String, ...), put(int, ...), put(Symbol, ...) now pass this (the proxy) as the 4th argument to the set trap.

2. NativeReflect: fix Reflect.construct() with LambdaConstructor

Reflect.construct used ctorBaseFunction.call() to invoke the target, but LambdaConstructor targets can be non-callable as they only support .construct() which would result in a TypeError when called.

Now we check if it's callable or constructable to decide what to do.

3. NativeReflect: re-implement Reflect.get() and Reflect.set() following official spec

The old implementation of Reflect.get and Reflect.set ignored the optional receiver parameter entirely.

[rbri]

Thanks a lot, but this requires some time, something for the weekend ;-)

[rbri]

first pr is on the way mozilla#2347

[rbri]

finally found the time to work on the ctor part - mozilla#2449

[rbri]

@duonglaiquang as far as i remember all these are now implemented. The ctor stuff is already merged into core-js, have added some more test and made a new snapshot build available. Will do a fresh htmlunit snapshot later tody.

Hopefully i have captured now all your open points, if not please wake me up....

Many, many thanks for all your contributions...