Add java.net.http package components to java2script.

[warownia1]

Java 11 introduced java.net.http package that adds fully functional http client to the standard library. It would be really nice to have it in java2script.
Here are some of the benefits of adding java.net.http to java2script:

• everyone has it, no extra dependencies needed
• no need to maintain and update it by yourself
• current javajs.http client has very limited functionality
• applications and libraries that want to support java2script could use java's native client instead of having hard dependency on javajs.http.HttpClient

[BobHanson]

@warownia1

Mateusz,

			if (!method.equals(METHOD_HEAD))
				conn.setDoInput(true);

I think true is just the default value, so this does nothing. I noticed recently that HEAD with setDoInput(false) gives no headers. But presumably with setDoInput(true) HEAD still does not send content or open a stream.