Introduce const into decompiler and stub builder

idea/testData/decompiler/decompiledText/Const.expected.kt

@@ -0,0 +1,9 @@
+// IntelliJ API Decompiler stub source generated from a class file
+// Implementation of methods is not available
+
+package test
+
+public object Const {
+    private const final val inObject: kotlin.Int /* compiled code */
+}
+

idea/testData/decompiler/decompiledText/Const/Const.kt

@@ -0,0 +1,5 @@
+package test
+
+object Const {
+    const private val inObject = 1
+}