Workaround copy bug for APFS volumes

[BobElDevil]

Fixes #1982

Drop down to the C api for copying files so we can avoid using the APFS
cloning functionality, which has a bug that can result in invalid
binaries

[BobElDevil]

If anyone knows how to programatically check whether we're on an APFS volume or not, I could make that check and only do this modified copy in that situation.

[jdhealy]

Awesome work on this, great stuff!

check whether we're on an APFS volume or not

Took some wrangling, but URLResourceKey.volumeSupportsFileCloningKey should indicate enough for us to avoid the bug.

Give me your comments on those commits, and pending your approval (of course), I can just push them right into this PR…

[BobElDevil]

Left some comments on the commits. Thanks for looking into the volume check

[jdhealy]

Changes are up.

Good notes on volumeSupportsFileCloning (now, func volumeSupportsFileCloning() throws -> Bool) — using a throwing method we actually lost some lines, despite improving error messaging. 🎉

[BobElDevil]

Looks good, you just missed changing the call site:
try from.volumeSupportsFileCloning.dematerialize()
Needs to be
try from.volumeSupportsFileCloning()

Then I think we're good to go

[mdiep]

I don't love that we have to do this, but it seems like this is a reasonable workaround. Thanks for tackling it! I'll let the two of you keep going with this and merge it. 👍

[BobElDevil]

I think we've each reviewed each others portion so I'm gonna go ahead and merge this 🎉