Less allocating IdentityResult.Failed overload

[N0D4N]

Background and Motivation

IdentityResult provides useful factory Failed method for creating failed IdentityResult, however it allocates array due to it accepting params IdentityError[] errors as argument, even if user passes only 1 error.
My proposal is to add overload to Failed method that will accept one IdentityError that will not allocate array in such case.

Proposed API

namespace Microsoft.AspNetCore.Identity;

public class IdentityResult
{
/*
		 Existing overload
    	 public static IdentityResult Failed(params IdentityError[] errors);
*/
+        public static IdentityResult Failed(IdentityError error);
}

Usage Examples

From user perspective nothing will change, the same method will be called, in the same way, unless they created params array explicitly;

// current
var result = IdentityResult.Failed();
result = IdentityResult.Failed(new IdentityError() // allocates array
					{
						Description = "Error description"
					});
result = IdentityResult.Failed(new IdentityError()
					{
						Description = "Error description"
					}, new IdentityError()
					{
						Description = "Error description2"
					});

// with proposed API
var result = IdentityResult.Failed();
result = IdentityResult.Failed(new IdentityError() // doesn't allocate array
					{
						Description = "Error description"
					});
result = IdentityResult.Failed(new IdentityError()
					{
						Description = "Error description"
					}, new IdentityError()
					{
						Description = "Error description2"
					});

Alternative Designs

Create overload accepting params Span<IdentityError> when/if dotnet/csharplang#1757 is implemented.

Risks

We would need to ensure that behavior of new overload is consistent with current overload, since after recompilation compiler will pick overload without params array, for cases when user calls Failed method with single error passed as argument. And behavior won't change unexpectedly for developer.

[adityamandaleeka]

Triage: this seems fairly low-value given the amount saved and the fact that it's not in a hot path.