Introduce const into decompiler and stub builder

idea/testData/stubs/Const.expected

@@ -0,0 +1,8 @@
+PsiJetFileStubImpl[package=test]
+  PACKAGE_DIRECTIVE:
+    REFERENCE_EXPRESSION:[referencedName=test]
+  IMPORT_LIST:
+  OBJECT_DECLARATION:[fqName=test.Const, isCompanion=false, isLocal=false, isObjectLiteral=false, isTopLevel=true, name=Const, superNames=[]]
+    CLASS_BODY:
+      PROPERTY:[fqName=test.Const.inObject, hasDelegate=false, hasDelegateExpression=false, hasInitializer=true, hasReturnTypeRef=false, isExtension=false, isTopLevel=false, isVar=false, name=inObject]
+        MODIFIER_LIST:[private const]

idea/testData/stubs/Const.kt

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