Implemented HiddenDeclaration annotation (doc-comment to be added!)

idea/idea-completion/testData/basic/multifile/HiddenDeclarations/HiddenDeclarations.dependency.kt

@@ -0,0 +1,14 @@
+package test
+
+@HiddenDeclaration
+fun hiddenFun(){}
+
+fun notHiddenFun(){}
+
+@HiddenDeclaration
+var hiddenProperty: Int = 1
+
+var notHiddenProperty: Int = 1
+
+@HiddenDeclaration
+val String.hiddenExtension: Int get() = 1

idea/idea-completion/testData/basic/multifile/HiddenDeclarations/HiddenDeclarations.kt

@@ -0,0 +1,16 @@
+package test
+
+@HiddenDeclaration
+fun hiddenFunFromSameFile(){}
+
+fun String.foo() {
+    hid<caret>
+}
+
+// INVOCATION_COUNT: 2
+// ABSENT: hiddenFun
+// ABSENT: hiddenProperty
+// ABSENT: hiddenFunFromSameFile
+// ABSENT: hiddenExtension
+// EXIST: notHiddenFun
+// EXIST: notHiddenProperty