Add proper type checking and type refinement for binding variables.

[smillst]

// @below-java17-jdk-skip-test
import org.checkerframework.checker.tainting.qual.Untainted;

public class TaintingBindingVariable {

  void bar1(@Untainted Object o) {
    if (o instanceof String s) {
      @Untainted String f = s;  // legal
    }
  }
  void bar2( Object o) {
    if (o instanceof @Untainted String s) { // error or warning?
      @Untainted String f = s;
    }
  }
}

There should be no errors in the bar1 method, but there should be an error or waring in the bar2 method.

[Rahulrajak1710]

I would like to work on this issue:)