New Rule T0035: Do not use var for this deconstruction

[pavel-mikula-sonarsource]

Coding style:

var pattern o is { P: var p } can be used only where o can be null and p is used at least 3 times.

if(something is { P: var p} // Noncompliant, used only twice
  && p > 0
  && p < 100)

The null requires SE knowledge. While we could implement it easily, it is probably too hard to plug ourselves into SE at the moment due to possible version mismatch.