[macOS] Archive universal gen_snapshot binaries

[cbracken]

In #53524, we started producing universal gen_snapshot_arm64 and gen_snapshot_x64 binaries. This migrates away from bundling gen_snapshot binaries with x64-only host architecture to universal binaries that bundle both x64 and arm64 host architectures.

Also adds a dependency on flutter/lib/snapshot:create_macos_gen_snapshots to the profile build, where it was previously missing. Presumably, gen_snapshot was being built as a side-effect of one of the other targets.

Issue: flutter/flutter#101138
Issue: flutter/flutter#69157

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[zanderso]

lgtm

you might run into trouble with this:

https://github.com/flutter/engine/blob/main/ci/builders/mac_ios_engine.json#L518

but I believe it is safe to delete, if so.

[cbracken]

I'm fairly convinced that gen_snapshot is the [suspected-]unused arm64-only gen_snapshot in the tool cache; I've got a followup that removes this to see if anything explodes, but my sense is that given this would have been unusable on Intel Macs for well over a year now, that we should have had bug reports from Intel Mac users by now if it were used.

Doing some testing since I could still imagine tool internals doing things like checking for an trying to re-cache it if missing.

[auto-submit]

auto label is removed for flutter/engine/53962, due to - The status or check suite Mac mac_host_engine has failed. Please fix the issues identified (or deflake) before re-applying this label.

[christopherfujino]

auto label is removed for flutter/engine/53962, due to - The status or check suite Mac mac_host_engine has failed. Please fix the issues identified (or deflake) before re-applying this label.

Whoops:

Cannot find gen_snapshot at /Volumes/Work/s/w/ir/cache/builder/src/out/ci/mac_profile_arm64/gen_snapshot_arm64

[cbracken]

Fixed: turns out we never actually depended on the lib/snapshots:create_macos_gen_snapshots target (or the archive target we used to depend on)... but only for profile mode. Therefore it didn't show up in my find-and-replace patch yesterday to swap the dependency to the create_macos_gen_snapshots target. The old unsuffixed one is build as a side-effect of one of the other targets being depended on, the new ones aren't.