We've adopted this pattern in Cranelift's instruction definitions where
we let-bind some calls to `Operand::new` and then later use them in one
or more calls to `Inst::new`.
That pattern has two problems:
- It puts the type of each operand somewhere potentially far removed
from the instruction in which it's used.
- We let-bind the same name for many different operands, compounding the
first problem by making it harder to find _which_ definition is used.
So instead this commit removes all let-bindings for operand definitions
and constructs a new `Operand` every time.
Constructing an `Operand` at every use means we duplicate some
documentation strings, but not all that many of them as it turns out.
I've left the let-bound type-sets alone, so those are currently still
shared across many instructions. They have some of the same problems and
should be reviewed as well.
f877141668