IDE. Allow expect declarations in completion in shared native modules

Issue #KMM-218

core/descriptors/src/org/jetbrains/kotlin/platform/TargetPlatform.kt

@@ -84,7 +84,15 @@ interface TargetPlatformVersion {
     }
 }
 
-fun TargetPlatform?.isCommon(): Boolean = this != null && size > 1 && iterator().let { i ->
+/**
+ * Whether this is a [TargetPlatform] that targets multiple [SimplePlatform]s.
+ */
+fun TargetPlatform?.isMultiPlatform(): Boolean = this != null && size > 1
+
+/**
+ * Whether this is "Common" platform in its classical sense (MPP v1).
+ */
+fun TargetPlatform?.isCommon(): Boolean = isMultiPlatform() && this!!.iterator().let { i ->
     val firstPlatformName = i.next().platformName
     while (i.hasNext()) {
         if (i.next().platformName != firstPlatformName) return@let true

idea/idea-completion/src/org/jetbrains/kotlin/idea/completion/CompletionSession.kt

@@ -39,7 +39,7 @@ import org.jetbrains.kotlin.idea.imports.importableFqName
 import org.jetbrains.kotlin.idea.project.TargetPlatformDetector
 import org.jetbrains.kotlin.idea.references.mainReference
 import org.jetbrains.kotlin.idea.util.*
-import org.jetbrains.kotlin.platform.isCommon
+import org.jetbrains.kotlin.platform.isMultiPlatform
 import org.jetbrains.kotlin.platform.jvm.isJvm
 import org.jetbrains.kotlin.psi.*
 import org.jetbrains.kotlin.resolve.BindingContext
@@ -151,7 +151,7 @@ abstract class CompletionSession(
             { CompletionBenchmarkSink.instance.onFlush(this) },
             prefixMatcher, parameters, resultSet,
             createSorter(), (file as? KtCodeFragment)?.extraCompletionFilter,
-            moduleDescriptor.platform.isCommon()
+            moduleDescriptor.platform.isMultiPlatform()
         )
     }