Add Big Sur-style macOS icons

[Leland]

Summary

Build "Add Big Sur-style macOS icons"

Purpose of change

I updated our macOS icons to higher quality resolutions in #23181, back in 2018. Since then, macOS has landed on "squircle" icons, and leaves vertical whitespace. CDDA's older icon caused it to really sit out of place in the dock as a result.

This PR adds such a backing to the macOS CDDA app icons. The sizes are all generated with our SVG, so they're crisp.

Describe the solution

N/A

Describe alternatives you've considered

N/A

Testing

N/A

Additional context

Before:

After:

[Leland]

Failing test looks fine...? I guess this is just flaky:

([slow] ~starting_items)=> ??:?
([slow] ~starting_items)=> Catch::RunContext::runTest(Catch::TestCase const&)
([slow] ~starting_items)=> ??:?
([slow] ~starting_items)=> Backtrace emission took 2 seconds.
([slow] ~starting_items)=> (continued from above) ERROR : src/item.cpp:1500 [ret_val item::put_in(const item&, item_pocket::pocket_type, bool)] tried to put an item (thermos) count (1) in a container (daypack) that cannot contain it: pockets unacceptable because item is too short, item too big, or not enough space27.572 s: shot_features