Value update operations

[BosqueLanguage]

Want to add update operation for tuples/records/ootypes. Should also include "in-place" support like:

var y = {f=1i, g=2i};
y.{g=5i};

[marron-at-work]

Also for ref methods we may want to have a special assignment operation:

let x = ...;
this<-x;

Where x is the same type as this. Will be useful for computing a new value functionally and then assigning it back (without needed to do an explicit assign of every field).