dillon1000/react

MutableIfOperandsAreMutable flag handles mutation via capturing

There was one missing piece to the optimization from the previous PR: Array#map 
can return an alias to the receiver in its output, which means that mutations of 
the result have to be treated as mutations of the receiver. This means we need 
to use a Capture effect on the receiver. If that doesn't get downgraded to a 
Read bc the value was immutable, we then also need to make the lvalue effect a 
Store (so that InferMutableRanges actually looks at it for aliasing).