Replace the binary `Operation` interfaces with the `OperationWith(T:!
type)` interfaces described in the design, and add a `Result` associated
type for both unary and binary operations. Update the `impl`s in the
prelude for integer types to use the new form, including supporting
implicit conversion of either operand.
I've tried to split this PR up into commits focused on distinct changes
for review convenience. It may be simplest to review it one commit at a
time.
Updating tests in the style of #5455.
array indexing requires integers, so this is a more prelude-dependent
area than some. But as it turns out, writing something like `3` never
references `Core.IntLiteral` so seeing if I can roll with more minimal
preludes.
Richard Smith
Jon Ross-Perkins