Add macOS test builders to CI

[dagood]

This PR adds macOS buildandpack to produce Go toolsets, but doesn't include the standard library tests:

• Support macOS (darwin) amd64 and arm64 builds of Microsoft Go #1368

In a test run I ran early on, devscript worked, but test didn't. (test may run additional tests, but it isn't quite longtest and should be reliable.)

https://dev.azure.com/dnceng/internal/_build/results?buildId=2575070&view=logs&j=1fc39dc4-3ae2-57e7-a254-ceccd9c00bb3&t=e8fde53a-663f-5432-3a67-c3eefd0bab24&l=200

panic: test timed out after 9m0s
	running tests:
		TestLookupNoSuchHost (8m58s)
		TestLookupNoSuchHost/LookupNS_NXDOMAIN (2m54s)
		TestLookupNoSuchHost/LookupNS_NXDOMAIN/forced_cgo_resolver (22s)

I didn't investigate at the time and decided to split it off into another issue. (I don't have a Mac.)

Tests that involve the network are suspect--our macOS test machines are probably different from upstream's macOS environments, and networking in particular can be tricky depending on the lab. Maybe I just got very unlucky, or maybe macOS needs retries like Windows.

If we can't figure this out for 1.24, we can consider removing the un-CI-tested macOS buildandpack jobs.