KT-2498 Bridge method is not generated for method when generic parameters are substituted in superclass

#KT-2498 Fixed

generateBridgeIfNeeded() now works as follows: for a given method, find
which declared methods does this method override via breadth-first search.
For each such declared method, generate a bridge if and only if its
signature is different. Keep different methods' signatures in a set to
avoid duplicated bridge signatures.

compiler/testData/codegen/bridges/simpleEnum.kt

@@ -0,0 +1,20 @@
+open enum class A<T> {
+    open fun foo(t: T) = "A"
+}
+
+enum class Z(val name: String) : A<String>() {
+    Z1 : Z("Z1")
+    Z2 : Z("Z2")
+    override fun foo(t: String) = name
+}
+
+
+fun box(): String {
+    return when {
+        Z.Z1.foo("")               != "Z1" -> "Fail #1"
+        Z.Z2.foo("")               != "Z2" -> "Fail #2"
+        (Z.Z1 : A<String>).foo("") != "Z1" -> "Fail #3"
+        (Z.Z2 : A<String>).foo("") != "Z2" -> "Fail #4"
+        else -> "OK"
+    }
+}