S2971: Split rule in multiple rules

[mary-georgiou-sonarsource]

Rule S2971 seems like multiple rules folded into one. It would be better to split the rule into multiple ones and re-evaluate.
This way users can enable and disable the parts that are useful to their codebase.

Potential split:

1. Use OfType instead of using Select with as to typecast elements and then null-checking in a query expression to choose elements based on type.
2. Use OfType instead of using Where and the is operator, followed by a cast in a Select
3. Use an expression in Any instead of Where(element => [expression]).Any().
4. Use Count instead of Count() when it’s available.
5. Don’t call ToArray() or ToList() in the middle of a query chain.

Related community post.