Completion for fqNames in KDoc links

Tests, also proved that KT-14432 are fixed
Added completion and tests for extension functions.

idea/idea-completion/testData/kdoc/ExtensionsFQLink.kt

@@ -0,0 +1,20 @@
+package a
+
+class B {
+    /**
+     * [a.B.<caret>]
+     */
+    fun member() {
+
+    }
+}
+
+fun B.ext() {
+
+}
+
+val B.extVal: String
+    get() = ""
+
+// EXIST: ext
+// EXIST: extVal

idea/idea-completion/testData/kdoc/ExtensionsForSubClassFQLink.kt

@@ -0,0 +1,33 @@
+package a
+
+class C {
+
+    class B {
+        /**
+         * [a.C.B.<caret>]
+         */
+        fun member() {
+
+        }
+    }
+
+    fun B.ext() {
+
+    }
+
+    val B.extVal: String
+        get() = ""
+}
+
+fun C.B.topExt() {
+
+}
+
+val C.B.topExtVal: String
+    get() = ""
+
+
+// EXIST: ext
+// EXIST: extVal
+// EXIST: topExt
+// EXIST: topExtVal

idea/idea-completion/testData/kdoc/FQLink.kt

@@ -0,0 +1,19 @@
+package z
+
+/**
+ * [z.<caret>]
+ */
+fun f(xyzzy: String) {
+
+}
+
+fun bar() {
+
+}
+
+class Z
+
+// EXIST: Z
+// EXIST: f
+// EXIST: bar
+// ABSENT: z

idea/idea-completion/testData/kdoc/Link.kt

@@ -1,3 +1,5 @@
+package z
+
 /**
  * [<caret>]
  */
@@ -9,5 +11,9 @@ fun bar() {
 
 }
 
+class Z
+
+// EXIST: z
+// EXIST: Z
 // EXIST: xyzzy
 // EXIST: bar

idea/idea-completion/testData/kdoc/MemberEnumEntryFQLink.kt

@@ -0,0 +1,11 @@
+package z
+
+/**
+ * [z.X.Y.<caret>]
+ */
+class X {
+    enum class Y { First, Second }
+}
+
+// EXIST: First
+// EXIST: Second

idea/idea-completion/testData/kdoc/MemberEnumEntryLink.kt

@@ -0,0 +1,9 @@
+/**
+ * [Y.<caret>]
+ */
+class X {
+    enum class Y { First, Second }
+}
+
+// EXIST: First
+// EXIST: Second