Backport of #118291 to release/10.0, which resolved #118053.

Removes the IEquatable constraint from the ThrowIfEqual and ThrowIfNotEqual methods in ArgumentOutOfRangeException.

• Allows these methods to be used with types that don't implement IEquatable, relying on EqualityComparer.Default.Equals for equality comparisons.
• This broadens the applicability of these methods without sacrificing functionality.

/cc @jeffhandley @IDisposable

Customer Impact

• Customer reported
• Found internally

• The IEquatable<T> constraint prevents customers from using the ThrowIfEqual and ThrowIfNotEqual methods on nullable value types (e.g., int?).
• This change will also allow customers to use the ThrowIfEqual and ThrowIfNotEqual methods to validate enum arguments:

Regression

• Yes
• No

Testing

Existing product code and test code was already using this method. New tests are added in #119263 that explicitly exercise the customer scenarios mentioned above.

Risk

Low. The implementation is unchanged with the removal of the constraint. As @tannergooding mentioned on the issue discussion, "We use EqualityComparer in many similar cases and for similar reasons, it is correspondingly optimized as [Intrinsic] by the runtime in several scenarios."