Remove some bounds checks around Vector.Create(Span)

[EgorBo]

let's see if this works..

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[EgorBo]

@MihuBot

[EgorBo]

This might work, but we need examples where Create(Span) is used to validate this. So far, there is only one use in the whole BCL - in IPAddress (that I recently added there) - everywhere else we use unsafe APIs to load/store vectors

[tannergooding]

This might work, but we need examples where Create(Span) is used to validate this. So far, there is only one use in the whole BCL - in IPAddress (that I recently added there) - everywhere else we use unsafe APIs to load/store vectors

@EgorBo, isn't this a bit of a "chicken and egg" problem? The BCL largely doesn't use these APIs because its unoptimized and so we won't get any hits when attempting to optimize it.

We could pick a couple simple examples in SpanHelpers and update them as part of the PR to validate the improvement (although that might negatively impact Mono) or provide a regression test and validate that gets good codegen improvements with this change. I think simply getting it to the point where we can optimize some cases is a good starting point and will let us make follow up iterative improvements, as well as push users towards using it in their code.