RSRP-288331: Allow InstantHandleAttribute on methods (to indicate the return value is not deferred)

We use IEnumerable<T> to represent an enumerable set of values, but there's no way to indicate that a method doesn't return a deferred query. For example, ReSharper will raise possible multiple enumeration of IEnumerable warnings for the code below:

public IEnumerable<int> GetRandomArray()
{
	return new[] { 4 };
}

public void Demo()
{
	IEnumerable<int> values = this.GetRandomArray();
	if(values.Any())
		Console.WriteLine(values.First());
}

This could be fixed by allowing InstantHandleAttribute to be placed on methods, which would indicate that the return values are not deferred:

[InstantHandle]
public IEnumerable<int> GetRandomArray()
{
	return new[] { 4 };
}