DFGArgumentsEliminationPhase should be able to get rid of allocations for NewArrayWithSpread made of other NewArrayWithSpread

[Robin Morisset]

I am thinking of code like the following (admittedly a bit artificial):
function f(...a) {
    var b = [...a, ...a];
    var c = [...b, 42, ...b]
    // do stuff with c here without letting it escape
}
There is no good reason for this code not to be optimized, but currently we only optimize NewArrayWithSpread if its Spread(s) come from a NewArrayBuffer or a CreateRest, and not if they come for example from a NewArrayWithSpread.