FIR IDE: introduce package symbol

idea/idea-frontend-api/src/org/jetbrains/kotlin/idea/frontend/api/symbols/KtPackageSymbol.kt

@@ -0,0 +1,12 @@
+/*
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * 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.kotlin.idea.frontend.api.symbols
+
+import org.jetbrains.kotlin.name.FqName
+
+abstract class KtPackageSymbol : KtSymbol {
+    abstract val fqName: FqName
+}