JS: add test to prove that #KT-5051 is no more reproducible

compiler/testData/diagnostics/testsWithJsStdLib/name/propertyAndMethodInImplementor.kt

@@ -0,0 +1,9 @@
+package foo
+
+interface I {
+    <!JS_NAME_CLASH!>fun foo()<!> = 23
+}
+
+class Sub : I {
+    <!JS_NAME_CLASH!>var foo<!> = 42
+}