Correct zero length check expressions

[MikeAlhayek]

I noticed many invalid expression used in OC when checking for a zero elements in a collection.

Here is explanation

List<string> items = null;

if(items?.Count == 0)
{
	// This will evaluate false since null does not equals 0.
}

if(items == null || items.Count == 0)
{
	// This will evaluate true since items either null OR is not null and it's count is 0.
}

if(items?.Count > 0)
{
	// This check is okay because null items will return false and if the Count is 0 will also false.
}

@Piedone it would be nice to add an analyzer to guard against such a count check. Maybe related to #7950

[github-actions]

This pull request has merge conflicts. Please resolve those before requesting a review.

[MikeAlhayek]

@gvkries feel free to leave code review and approve PRs when you visit them

[Piedone]

FYI I checked if the more succinct items?.Any() == false pattern would work. It wouldn't, as it (I don't understand why) produces null; and it also violates CA1860, nudging you towards items?.Count == 0. So, that's not an option.