C#: Update query to handle static field writes from properties.

[michaelnebel]

It turns out that the query cs/static-field-written-by-instance reports false positives if a static property writes to static field.
That is, the example below leads to a false positive. This is fixed in this PR.

static object backingField;
static object StaticProp
{
    get
    {
        return backingField ?? (backingField = new object()); // OK
    }
}

[mbg]

One question and one suggestion, otherwise looks good.

[mbg]

Question: could this be implemented like this:

Suggested change

	not exists(Member m | m = c or m = c.(Accessor).getDeclaration() | m.isStatic()) and
	not (c.(Member).isStatic() or c.(Accessor).getDeclaration().isStatic()) and

and would that (potentially) be better for performance?

[hvitved]

Or even shorter

not [c.(Member), c.(Accessor).getDeclaration()].isStatic()

[michaelnebel]

Yes, it can be implemented like this, but I don't think that it will have any effect on performance.
I prefer the original solution as it re-uses the isStatic logic across the relevant members.
I prefer Toms suggestion.