Provide replacement for methods deprecated in favor of SAM-constructors.

Provide replacement for isNotEmpty on nullable receiver.
JS: Provide SAM-like constructor for Runnable.

js/js.libraries/src/core/javalang.kt

@@ -29,6 +29,10 @@ public trait Runnable {
     public open fun run() : Unit;
 }
 
+public fun Runnable(action: () -> Unit): Runnable = object : Runnable {
+    override fun run() = action()
+}
+
 library
 public trait Appendable {
     public open fun append(csq: CharSequence?): Appendable