avoid this-bound method closure creation when using method.bind

[nadako]

This is better illustrated with an example:

class C {
	public function new() {
		run(process.bind(42));
	}

	public function run(f:()->Void) {
		f();
	}

	public function process(value:Int) {
		trace(value);
	}
}

function main() {
	new C();
}

this will generate the following JS (although I'm pretty sure it's not js-specific, since the method closure must be created on all platforms)

let _g = $bind(this,this.process);
let value = 42;
this.run(function() {
	_g(value);
});

we have two closures here: the one comes from $bind, and the one from .bind-ing that to actual arguments. but the first one is redundant and we could instead generate

let _gthis = this;
let value = 42;
this.run(function() {
	_gthis.process(value);
});