Optimize object literals

[bnoordhuis]

function o(x,y,z){ return {x,y,z} }

Produces bytecode that sets the fields 1-by-1:

;; function o(x, y, z) { return {x, y, z} }

        object         
        get_arg0        0    ; x
        define_field    x
        get_arg1        1    ; y
        define_field    y
        get_arg2        2    ; z
        define_field    z
        return         

It should be more efficient to use an "object template" that describes what properties the object has:

;; function o(x, y, z) { return {x, y, z} }

        get_arg0        0    ; x
        get_arg1        1    ; y
        get_arg2        2    ; z
        define_object <id>   ; ( x y z -- o )
        return         

Benefits:

• reduces bytecode size
• object layout is known upfront, don't have to update JSShape repeatedly