JetDiagnosticsTest migrated to TestGenerator

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

compiler/testData/diagnostics/tests/GenericFunctionIsLessSpecific.kt

@@ -0,0 +1,8 @@
+// A generic funciton is always less specific than a non-generic one
+fun foo<T>(<!UNUSED_PARAMETER!>t<!> : T) : Unit {}
+fun foo(<!UNUSED_PARAMETER!>i<!> : Int) : Int = 1
+
+fun test() {
+    foo(1) : Int
+    foo("s") : Unit
+}