[JS IR] Add tests for JS code KLIB diagnostics

^KT-62425

compiler/testData/diagnostics/testsWithJsStdLibAndBackendCompilation/jsCode/javaScriptEmpty.kt

@@ -0,0 +1,19 @@
+// FIR_IDENTICAL
+// ERROR_POLICY: SEMANTIC
+
+fun testEmptyString() {
+    js(<!JSCODE_NO_JAVASCRIPT_PRODUCED!>""<!>)
+}
+
+const val SPACE = " "
+
+fun testStringWithSpaces() {
+    js(<!JSCODE_NO_JAVASCRIPT_PRODUCED!>"\n \n$SPACE \t" + " "<!>)
+}
+
+fun testComment() {
+    js(<!JSCODE_NO_JAVASCRIPT_PRODUCED!>"""
+        // just a comment
+        $SPACE
+    """<!>)
+}