Sort move instructions on the Y register

Sort sequences of `move` instructions on the Y register.

When moving from X registers to Y registers, having the instructions
sorted on Y registers give the loader more opportunities to use
`move_window{3,4,5}` instructions. For examples, the following five
instructions:

    move_xy x(2) y(0)
    move_xy x(1) y(1)
    move_xy x(0) y(2)
    move_xy x(5) y(3)
    move_xy x(4) y(4)

can be replaced with:

    move_window5_xxxxxy x(2) x(1) x(0) x(5) x(4) y(0)

When the Y registers are not ordered so that `move_window5` can be
used, the loader would typically combine the first three moves to a
`move3_xyxyxy` instruction and the last two moves to a
`move2_par_xyxy` instruction.

When moving from Y registers to X registers, sorting on the Y
registers could potentially be more cache-friendly. It could also
be worthwhile investigating a new `move_window` instruction in
the BEAM interpreter that could move values from contiguous Y registers
to X registers.

Note that `scripts/diffable` can generate diffable dissambly files for
the loaded BEAM code:

    $ scripts/diffable --dis 0
    $ scripts/diffable --dis 1
    $ diff -u 0 1

0 files changed, 0 insertions, 0 deletions