Explicitly demarcate platform support

[notgull]

As discussed in today's meeting, this commit creates two tiers of
support. Tier 1, which is what we actively test, and Tier 2, what we
hope compiles.

[kchibisov]

Should probably put it in a separate file, since we'll remove the FEATURES.md and then probably should also include it in the docs somehow?

[notgull]

Should probably put it in a separate file, since we'll remove the FEATURES.md and then probably should also include it in the docs somehow?

Done and done

[notgull]

For the initial draft here I've gone with more platforms than we probably need. I think all the tier 1's are necessary, since we actively test them in CI and they directly correspond to the canonical versions of the winit backend's platforms.

For the tier 2's:

• ARM windows is becoming more popular, so we should make sure our bases are covered there.
• Do we want to support Windows 7? I added it here for discussion. I think we should, since lots of computers (especially old ones) still run Win7.
• Alpine Linux is sufficiently popular that I think we should be building musl. Same with FreeBSD. Not sure about NetBSD but issues have been filed on it in the past so I've added it.
• Other architecture Linux is fair game. I think we should be building ARM, I can take or leave the rest.

[madsmtm]

Approved once the data is deduplicated somehow (see first comment)

[daxpedda]

I think this requires a tier 3?
E.g. tier 2 is actually tested in CI, tier 3 is not but we believe it should work?
Unless we want to actually just go ahead and test them in CI (which I would be in favor of), then we should do this right here.

Or am I missing something?

[daxpedda]

I went ahead and adjusted the wording around Web as I suggested.