do not generate delegates when the class already has such method either declared or delegated (report an ambiguity in this case)

Merge conflict resolved by committer

compiler/testData/diagnostics/tests/Delegation_MultipleDelegates.kt

@@ -0,0 +1,18 @@
+trait One {
+  public open fun foo() : Int
+  private fun boo() = 10
+}
+trait Two {
+  public open fun foo() : Int
+}
+
+trait OneImpl : One {
+  public override fun foo() = 1
+}
+trait TwoImpl : Two {
+  public override fun foo() = 2
+}
+
+class <!MANY_IMPL_MEMBER_NOT_IMPLEMENTED!>Test1<!>() : TwoImpl, OneImpl {}
+class Test2(a : One) : One by a, Two {}
+class <!MANY_IMPL_MEMBER_NOT_IMPLEMENTED!>Test3<!>(a : One, b : Two) : Two by b, One by a {}