JetDiagnosticsTest migrated to TestGenerator

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

compiler/testData/diagnostics/tests/regressions/Jet124.kt

@@ -0,0 +1,8 @@
+fun foo1() :  (Int) -> Int = { (x: Int) -> x }
+
+fun foo() {
+  val h :  (Int) -> Int = foo1();
+  h(1)
+  val m :  (Int) -> Int = {(a : Int) -> 1}//foo1()
+  m(1)
+}