One-shot hash feedback

[vcsjones]

This addresses the feedback from #17590.

I wasn't able to find any good examples of "Use this Win32 API if it's available, otherwise emulate it". If there is a example to model that off of other than what I did, happy to re-do the approach.

Fixes #17590.

[ghost]

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[bartonjs]

Suggested change

	private static volatile bool s_UseCompatOneShot;
	private static volatile bool s_useCompatOneShot;

[bartonjs]

You marked this as fixing the issue, but it isn't doing the EVP algorithm handle caching.

(The easiest fix on that is to just change the internal methods to something like if (s_evpSha1 == IntPtr.Zero) { s_evpSha1 = RealEvpSha1ShimCall(); Debug.Assert(s_evpSha1 != IntPtr.Zero); } return s_evpSha1;)

[vcsjones]

@bartonjs Was this change perhaps overlooked, or am I holding it wrong? https://github.com/dotnet/runtime/pull/39372/files#diff-283eaf9255778de038e266b90f9bea05R32

[bartonjs]

Ah, looks like the notification I opened was for the second commit being pushed, instead of the root of the PR. I feel better now as to why it wasn't on my screen, but am nonetheless embarrassed and apologetic.

Since I don't see any other calls to those interop methods the place you decided to cache them seems fine.

[vcsjones]

All good! As always I appreciate the quick and thorough reviews.