Change the muli-return syntax for operations. The name of the operation result...

Change the muli-return syntax for operations. The name of the operation result now contains the number of results that it refers to if the number of results is greater than 1.

Example:
    %call:2 = call @multi_return() : () -> (f32, i32)
    use(%calltensorflow/mlir#0, %calltensorflow/mlir#1)

This cl also adds parser support for uniquely named result values. This means that a test writer can now write something like:
    %foo, %bar = call @multi_return() : () -> (f32, i32)
    use(%foo, %bar)

Note: The printer will still print the collapsed form.
PiperOrigin-RevId: 240860058