JetDiagnosticsTest migrated to TestGenerator

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

compiler/testData/diagnostics/tests/QualifiedExpressions.kt

@@ -0,0 +1,13 @@
+package qualified_expressions
+
+fun test(s: String?) {
+   val <!UNUSED_VARIABLE!>a<!>: Int = <!TYPE_MISMATCH!>s?.length<!>
+   val b: Int? = s?.length
+   val <!UNUSED_VARIABLE!>c<!>: Int = s?.length ?: -11
+   val <!UNUSED_VARIABLE!>d<!>: Int = s?.length ?: <!TYPE_MISMATCH!>"empty"<!>
+   val e: String = <!TYPE_MISMATCH!>s?.length<!> ?: "empty"
+   val <!UNUSED_VARIABLE!>f<!>: Int = s?.length ?: b ?: 1
+   val <!UNUSED_VARIABLE!>g<!>: Boolean? = e.startsWith("s")//?.length
+}
+
+fun String.startsWith(<!UNUSED_PARAMETER!>s<!>: String): Boolean = true