Implement Kotlin Script support in UAST

#KT-18353 Fixed

plugins/uast-kotlin/testData/SimpleScript.kts

@@ -0,0 +1,20 @@
+println("Hello World!")
+
+fun getBarOrNull(flag: Boolean): Bar? {
+    return if (flag) Bar(42) else null
+}
+
+class Bar(val a: Int) {
+    val b: Int = 0
+
+    fun getAPlusB() = a + b
+
+    class Baz {
+        fun doSomething() {
+
+        }
+    }
+}
+
+getBarOrNull(true)
+println("Goodbye World!")