add IsOSPlatformOrLater and IsOSPlatformEarlierThan methods

[adamsitnik]

Contributes to #33331

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[adamsitnik]

The spec mentions that:

The IsPlatformXXx methods should be recognized by the JIT to be constant

@tannergooding@jkotas could you please point me to some doc|PR that explains|shows how to make JIT recognize given method as a constant?

[tannergooding]

I'm not sure the JIT treating them as a constant is necessarily a .NET 5 goal, but rather an eventual goal.

I don't think getting the JIT to support ISOSPlatform is going to necessarily be trivial as I believe IsOSPlatform would need to be intrinsic, as would the OSPlatform.Windows and related properties.

Jan or someone else may know better or have a different opinion here, of course 😄

[jkotas]

I agree with @tannergooding that the design of these APIs is unfriendly to optimizations, and recognizing the complex pattern as constant would be non-trivial. I do not think we should be building one-off optimizations like that.

If somebody needs to call this on a hot path, they should cache the result in a static readonly bool.

[buyaa-n]

I think we should add other new OS versions with this PR EDIT: there is another PR for this. LGTM, thanks!