[michaelnebel]

In this PR we introduce data flow support for implicit deconstruct calls.

The example below is valid C# syntax and the assignment var (x, y) = r implicitly invokes the compiler generated Deconstruct method on r.

public record R(string S, object O)
...
var r = new R("S", new object())
var (x, y) = r

The last assignment is equivalent to

r.Deconstruct(out var x0, out var y0)
var (x, y) = (x0, y0).

The QL implementation contains the following

• Predicate for identifying expressions where deconstruct is implicitly called.
• Synthetic data flow nodes for the deconstruct call, the deconstruct out parameters (and the receiver argument node for the synthetic call).
• Flow summaries for compiler generated deconstruct methods.
• Only deconstruct calls in assignments and pattern matching are covered in this PR.

Furthermore, there is also the following limitations

• Only one level of deconstruct supported.
• Deconstruct extension methods are not supported.
• Foreach loop variable assignment is not covered.

Note, that value tuples don't have a deconstruct method and the tuple classes have deconstruct extension methods. If we want replace the existing tuple logic, we need to support deconstruct extension methods and support nested deconstructs.