KT-4976 Completion ignores smart casts

#KT-4976 Fixed
 #KT-5718 Fixed

idea/testData/completion/basic/multifile/ExtensionsForAutoCasted/ExtensionsForAutoCasted.dependency.kt

@@ -0,0 +1,4 @@
+package other
+
+public val String.extensionPropNotImported: Int
+    get() = 1

idea/testData/completion/basic/multifile/ExtensionsForAutoCasted/ExtensionsForAutoCasted.kt

@@ -0,0 +1,11 @@
+val String.extensionProp1: Int get() = 1
+val String.extensionProp2: Int get() = 1
+
+fun foo(o: Any) {
+    if (o !is String) return
+    o.ext<caret>
+}
+
+// EXIST: extensionProp1
+// EXIST: extensionProp2
+// EXIST: extensionPropNotImported