FIR: introduce package directive

The package directive is needed for KtElement -> FirElement mapping in IDE.
There should be some FirElement which will be result of mapping of elements
inside KtPackageDirective.

compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/FirTreeBuilder.kt

@@ -56,6 +56,7 @@ object FirTreeBuilder : AbstractFirTreeBuilder() {
     val propertyAccessor = element("PropertyAccessor", Declaration, function, contractDescriptionOwner, typeParametersOwner)
     val constructor = element("Constructor", Declaration, function, typeParameterRefsOwner)
     val file = element("File", Declaration, annotatedDeclaration)
+    val packageDirective = element("PackageDirective", Other)
 
     val anonymousFunction = element("AnonymousFunction", Declaration, function, typeParametersOwner)
     val anonymousFunctionExpression = element("AnonymousFunctionExpression", Expression, expression)

compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/NodeConfigurator.kt

@@ -389,13 +389,17 @@ object NodeConfigurator : AbstractFieldConfigurator<FirTreeBuilder>(FirTreeBuild
         }
 
         file.configure {
+            +field("packageDirective", packageDirective)
             +fieldList(import).withTransform()
             +declarations.withTransform()
             +stringField("name")
-            +field("packageFqName", fqNameType)
             +symbol("FirFileSymbol")
         }
 
+        packageDirective.configure {
+            +field("packageFqName", fqNameType)
+        }
+
         import.configure {
             +field("importedFqName", fqNameType, nullable = true)
             +booleanField("isAllUnder")