Bridges (#240)

* - bridges building
- bridges support in vtable and methods table

* FunctionDescriptor.signature fix + some assertions

* tests

* refactoring

* refactoring

* removed debug output

* refactoring

* review fixes

* implemented bridge construction for parameters

* tests

* refactoring

* removed custom box/unbox

* added bridge for extension receiver

backend.native/tests/codegen/bridges/test7.kt

@@ -0,0 +1,30 @@
+// generic interface, non-generic impl, vtable call + interface call
+open class A {
+    open var size: Int = 56
+}
+
+interface C<T> {
+    var size: T
+}
+
+open class B : C<Int>, A()
+
+fun box(): String {
+    val b = B()
+    if (b.size != 56) return "fail 1"
+
+    b.size = 55
+    if (b.size != 55) return "fail 2"
+
+    val c: C<Int> = b
+    if (c.size != 55) return "fail 3"
+
+    c.size = 57
+    if (c.size != 57) return "fail 4"
+
+    return "OK"
+}
+
+fun main(args: Array<String>) {
+    println(box())
+}