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/simpleObject.kt

@@ -0,0 +1,21 @@
+open class A<T> {
+    open fun foo(t: T) = "A"
+}
+
+object Z : A<String>() {
+    override fun foo(t: String) = "Z"
+}
+
+
+fun box(): String {
+    val z = object : A<String>() {
+        override fun foo(t: String) = "z"
+    }
+    return when {
+        Z.foo("")               != "Z" -> "Fail #1"
+        z.foo("")               != "z" -> "Fail #2"
+        (Z : A<String>).foo("") != "Z" -> "Fail #3"
+        (z : A<String>).foo("") != "z" -> "Fail #4"
+        else -> "OK"
+    }
+}