Optimize type checking for common cases

- Type equality for simple constructors (no arguments)
- Subtyping on final classes

compiler/testData/resolve/LocalObjects.resolve

@@ -3,7 +3,7 @@ package localObjects {
     ~x~val x : Int
   }
 
-  class Foo {
+  open class Foo {
     ~foo()~fun foo() : Int
   }
 

compiler/testData/resolve/Objects.resolve

@@ -1,6 +1,6 @@
 package toplevelObjectDeclarations
 
-class Foo(y : Int) {
+open class Foo(y : Int) {
   ~foo()~open fun foo() : Int = 1
 }
 

compiler/testData/resolve/ResolveOfInfixExpressions.resolve

@@ -40,7 +40,7 @@ fun f_plus(): Int {
   1 `contains`!in x
 }
 
-~Foo~class Foo {
+open ~Foo~class Foo {
   ~set1~fun set(i : Int, val1 : String) {}
   ~get1~fun get(i : Int) : Int {}
   ~get2~fun get(i : Int, j : Int) : String {}
@@ -92,4 +92,4 @@ fun testUnitIncDec() {
   var x = UnitIncDec()
   x`uinc`++
   x`udec`--
-}
+}