JetDiagnosticsTest migrated to TestGenerator

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

compiler/testData/diagnostics/tests/shadowing/ShadowParameterInNestedBlockInFor.kt

@@ -0,0 +1,7 @@
+fun f(<!UNUSED_PARAMETER!>i<!>: Int) {
+    for (j in 1..100) {
+        <!UNUSED_FUNCTION_LITERAL!>{
+            var <!NAME_SHADOWING, UNUSED_VARIABLE!>i<!> = 12
+        }<!>
+    }
+}