Minor. Move serialization annotation fq-names to IDE light-classes

They are a kind of a hack applied in light-classes and it'd be nice
to prevent them being used in irrelevant contexts

kotlin-serialization-compiler module should not depend on idea,
thus we can't use annotations directly there.

So, we copy-paste them and add a test on names consistency

plugins/kotlin-serialization/kotlin-serialization-ide/build.gradle.kts

@@ -20,7 +20,7 @@ dependencies {
 
 sourceSets {
     "main" { projectDefault() }
-    "test" {}
+    "test" { projectDefault() }
 }
 
 runtimeJar()

plugins/kotlin-serialization/kotlin-serialization-ide/test/org.jetbrains.kotlinx.serialization.idea/AnnotationNamesConsistencyTest.kt

@@ -0,0 +1,18 @@
+/*
+ * Copyright 2010-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license
+ * that can be found in the license/LICENSE.txt file.
+ */
+package org.jetbrains.kotlinx.serialization.idea
+
+import junit.framework.TestCase
+import org.jetbrains.kotlin.idea.caches.lightClasses.annotations.KOTLINX_SERIALIZABLE_FQ_NAME
+import org.jetbrains.kotlin.idea.caches.lightClasses.annotations.KOTLINX_SERIALIZER_FQ_NAME
+import org.jetbrains.kotlinx.serialization.compiler.resolve.SerializationAnnotations
+
+
+class AnnotationNamesConsistencyTest : TestCase() {
+    fun testConsistency() {
+        assertEquals(KOTLINX_SERIALIZABLE_FQ_NAME, SerializationAnnotations.serializableAnnotationFqName)
+        assertEquals(KOTLINX_SERIALIZER_FQ_NAME, SerializationAnnotations.serializerAnnotationFqName)
+    }
+}