Overloading operations via extension functions.

Also inline useless TranslationUtils#zeroLiteral. Eliminate dead code.

js/js.translator/testFiles/operatorOverloading/cases/overloadPlusAssignViaExtensionFunction.kt

@@ -0,0 +1,16 @@
+package foo
+
+import java.util.*
+
+fun <T> ArrayList<T>.plusAssign(other: Collection<T>) {
+    addAll(other)
+}
+
+fun box(): Boolean {
+    var v1 = ArrayList<String>()
+    val v2 = ArrayList<String>()
+    v1.add("foo")
+    v2.add("bar")
+    v1 += v2
+    return (v1.size() == 2 && v1[0] == "foo" && v1[1] == "bar")
+}

js/js.translator/testFiles/operatorOverloading/cases/overloadPlusAssignViaPlusExtensionFunction.kt

@@ -0,0 +1,19 @@
+package foo
+
+import java.util.*
+
+fun <T> ArrayList<T>.plus(other: Collection<T>): List<T> {
+    val c = ArrayList<T>()
+    c.addAll(this)
+    c.addAll(other)
+    return c
+}
+
+fun box(): Boolean {
+    var v1 = ArrayList<String>()
+    val v2 = ArrayList<String>()
+    v1.add("foo")
+    v2.add("bar")
+    v1 += v2
+    return (v1.size() == 2 && v1[0] == "foo" && v1[1] == "bar")
+}

js/js.translator/testFiles/operatorOverloading/cases/overloadPlusViaExtensionFunction.kt

@@ -0,0 +1,20 @@
+package foo
+
+import java.util.*
+
+fun <T> ArrayList<T>.plus(other: Collection<T>): List<T> {
+    val c = ArrayList<T>()
+    c.addAll(this)
+    c.addAll(other)
+    return c
+}
+
+fun box(): Boolean {
+    var v1 = ArrayList<String>()
+    v1.add("foo")
+    val v2 = ArrayList<String>()
+    v2.add("bar")
+    val v = v1 + v2
+
+    return (v.size() == 2 && v[0] == "foo" && v[1] == "bar")
+}

js/js.translator/testFiles/operatorOverloading/cases/overloadUnaryOperationsViaExtensionFunctions.kt

@@ -0,0 +1,12 @@
+package foo
+
+class A(val c: Int) {}
+
+
+fun A.inc() = A(5)
+fun A.dec() = A(10)
+
+fun box(): Boolean {
+    var a = A(1)
+    return ((++a).c == 5 && (a++).c == 5 && (--a).c == 10 && (a--).c == 10)
+}