C#: Read-only property flow.

[michaelnebel]

Dataflow for "readonly" properties (properties with only a "getter") didn't work.
That is, Obj = o wasn't detected as a store step into the property Obj. This is fixed in this PR.

public class C
{
    public object Obj { get; }

    public C(object o)
    {
        Obj = o;
    }
}

[michaelnebel]

DCA found some extra results (in test projects). I checked 2/3 using the information directly available in DCA and it looks like both these new results propagates information via property with only a getter, which looks correct.

[tamasvajk]

I think a change note should be added. This change might have a large impact on the number of issues found.

[hvitved]

LGTM

[michaelnebel]

Considering all the complicated stuff with primary constructors and getting that to work - this PR might have much larger impact 😭 .