C#: LINQ recommendation queries.

[michaelnebel]

In this PR we fix an issue with the LINQ recommendation queries.
The LINQ related queries provide suggestions for re-writes of foreach statements

foreach (type x in exp) {
...
}

where the exp is considered enumerable.

The expression exp is considered enumerable if either

• type implements the IEnumerable or IEnumerable<T> interface.
• type implements a public instance method GetEnumerator().

However, the LINQ extension methods are only defined on types implementing either the IEnumerable or IEnumerable<T> interface.
More specifically,

• Select, All and Where are extension methods on IEnumerable<T>
• Cast and OfType are extension methods in IEnumerable.

Furthermore, single dimensional arrays (arrays of rank 1) also implement the IEnumerable<T> interface: https://learn.microsoft.com/en-gb/dotnet/api/system.array?view=netframework-4.7#remarks

That is, we need to narrow the LINQ recommendation to only those cases.

[michaelnebel]

After inspecting the first DCA run it became evident that the initial version of the narrowing of the LINQ recommendations was to conservative. I have changed the implementation and re-based the PR. Let's see what DCA says before spending more time on review'ing.

[michaelnebel]

This time the reduction in results look more accurate.
I checked all the differences for the Powershell project and the removed results where indeed false positives. Furthermore, I checked the single removed result for the MissedAllOpportunity for the dotnet runtime and this was indeed also a false positive.

[michaelnebel]

DCA reports a slowdown for the Jetbrains re-sharper plugin, but I can't reproduce it locally. The logs also look fine. Overall I think the change is good.