[JS IR] Lower lambdas into in-line anonymous functions when possible

Previously we always generated factories for contextful lambdas:

```kt
fun foo(a: Int) = { a }
```

```js
function foo(a_38) {
  return foo$lambda(a_38);
}

// factory!
function foo$lambda($a) {
  return function () {
    return $a;
  };
}
```

After this patch, the generated code for `foo` is more concise:

```js
function foo(a) {
  return function() { return a; };
}
```

js/js.tests/tests-gen/org/jetbrains/kotlin/js/test/BoxJsTestGenerated.java

@@ -356,6 +356,12 @@ public class BoxJsTestGenerated extends AbstractBoxJsTest {
             runTest("js/js.translator/testData/box/closure/closureArrayListInstance.kt");
         }
 
+        @Test
+        @TestMetadata("closureCodeSize.kt")
+        public void testClosureCodeSize() throws Exception {
+            runTest("js/js.translator/testData/box/closure/closureCodeSize.kt");
+        }
+
         @Test
         @TestMetadata("closureFunctionAsArgument.kt")
         public void testClosureFunctionAsArgument() throws Exception {

js/js.tests/tests-gen/org/jetbrains/kotlin/js/test/ir/IrBoxJsTestGenerated.java

@@ -356,6 +356,12 @@ public class IrBoxJsTestGenerated extends AbstractIrBoxJsTest {
             runTest("js/js.translator/testData/box/closure/closureArrayListInstance.kt");
         }
 
+        @Test
+        @TestMetadata("closureCodeSize.kt")
+        public void testClosureCodeSize() throws Exception {
+            runTest("js/js.translator/testData/box/closure/closureCodeSize.kt");
+        }
+
         @Test
         @TestMetadata("closureFunctionAsArgument.kt")
         public void testClosureFunctionAsArgument() throws Exception {