8015270: @Contended: fix multiple issues in the layout code Summary: field count handling fixed, has_nonstatic_fields invariant fixed, oop map overrun fixed; new asserts Reviewed-by: kvn, dcubed, coleenp

// I can cast any old thing I want to this type object:
public class You_Have_Been_P0wned {
  // Make a bunch of int-fields so I can peek & poke it
  int _a;
  int _b;
  int _c;
  int _d;

}