Add fast paths to WhenAny(IEnumerable)

[Bond-009]

Adds fast paths in case tasks is an array or an ICollection

Fixes#26695

[dnfadmin]

All CLA requirements met.

[Wraith2]

Can you provide BenchmarkDotnet numbers showing the performance increase please?

[Bond-009]

I could, any guides on how to do this on linux?
IMHO, they shouldn't be needed.

1. This is almost exactly the same code as WhenAll(IEnumerable)
2. It prevents multiple allocations from the growing list in case the collection is an Array or an ICollection

[Wraith2]

https://benchmarkdotnet.org/ works on Linux just as well as windows. Just follow the docs.
Proof is almost always required for performance related changes because even though it may look like something is better it can make them worse. There is a performance repo tracking the perf of the runtime and bcl at https://github.com/dotnet/performance which may already have some benchmarks you can use.

[stephentoub]

Thanks.

[danmoseley]

Unrelated crypto failure, too old now for an issue?