all: make darwin/arm64 a first-class port

[bradfitz]

I assume that darwin/arm64 is now also a first-class port as of Go 1.16?

Add it to the list at https://github.com/golang/go/wiki/PortingPolicy#first-class-ports ?

/cc @dmitshur (who I just saw edit that page)

[dmitshur]

I read over #41385 and #38485, and I didn't see us making a decision on this (we may have agreed verbally in meetings).

It seems very reasonable. I think the port is meeting the three documented properties by now:

• we treat critical darwin/arm64 issues as release-blocking (this is my understanding, but worth confirming what others think)
• we provide official binaries (x/build/cmd/releasebot: provide binary release for darwin/arm64 for 1.16 #42756), and
• the installation is documented at https://golang.org/doc/install (although this page may need to be updated slightly, I don't think it suggests the darwin/arm64 installer yet; filed x/website/content/static/doc: install.html doesn't show darwin-arm64.pkg installer to Apple silicon users #43815).

I don't have concerns about graduating darwin/arm64 to be a first class port from my side. (Since darwin/amd64 is already a first class port, this is really more about "when" rather than "if".)

Since making any port a first class port requires a commitment from the entire Go team, let's make this a proposal (like #35593 was, to keep up the precedent), so others on the team can participate before we commit to a decision. (It'll take longer, but I don't think there's any rush here.)

CC @golang/release, @cherrymui, @aclements, @FiloSottile, @rsc.

[rsc]

We're already distributing binaries, so this is a first-class port. Let's update the docs. Thanks!

[dmitshur]

Done in wiki commit 87f61988.