KT-10770 IDEA cannot keep import if a type is only referenced by kdoc.

#KT-10770 Fixed

idea/testData/editor/optimizeImports/KDocReference.kt

@@ -0,0 +1,12 @@
+// RUNTIME
+import kotlin.concurrent.fixedRateTimer
+import kotlin.concurrent.read
+import java.util.ArrayList
+
+/**
+ * Reference to [ArrayList]
+ * Reference to [fixedRateTimer]
+ * Reference to [kotlin.concurrent.read]
+ */
+fun foo() {
+}

idea/testData/editor/optimizeImports/KDocReference.kt.after

@@ -0,0 +1,11 @@
+// RUNTIME
+import java.util.ArrayList
+import kotlin.concurrent.fixedRateTimer
+
+/**
+ * Reference to [ArrayList]
+ * Reference to [fixedRateTimer]
+ * Reference to [kotlin.concurrent.read]
+ */
+fun foo() {
+}