FIR IDE: handle reference to package and outer classes

For a qualified name like `foo.bar.Outer.Inner`, FIR represents it as
one atomic FIR element. Hence, to properly resolve these names to the
corresponding package and class, we need some additional work.

compiler/fir/tree/src/org/jetbrains/kotlin/fir/declarations/FirDeclarationUtil.kt

@@ -116,6 +116,12 @@ fun FirRegularClassBuilder.addDeclarations(declarations: Collection<FirDeclarati
 
 val FirTypeAlias.expandedConeType: ConeClassLikeType? get() = expandedTypeRef.coneTypeSafe()
 
+val FirClassLikeDeclaration<*>.classId
+    get() = when (this) {
+        is FirClass<*> -> symbol.classId
+        is FirTypeAlias -> symbol.classId
+    }
+
 val FirClass<*>.classId get() = symbol.classId
 
 val FirClassSymbol<*>.superConeTypes