JetDiagnosticsTest migrated to TestGenerator

- test data files renamed from *.jet to *.kt

compiler/testData/diagnostics/tests/override/SuspiciousCase1.kt

@@ -0,0 +1,12 @@
+// NamedFunctionDescriptor.substitute substitutes "overrides"
+// this test checks it does it properly
+
+trait Foo<P> {
+    fun quux(p: P, q: Int = 17) : Int = 18
+}
+
+trait Bar<Q> : Foo<Q>
+
+abstract class Baz() : Bar<String>
+
+fun zz(b: Baz) = b.quux("a")