FIR: handle double-imported qualifiers properly

compiler/testData/diagnostics/tests/imports/DoubleImports.kt

@@ -3,7 +3,9 @@
 
 package star
 
-class SomeClass
+class SomeClass {
+    class Nested
+}
 
 fun foo() {}
 
@@ -32,6 +34,8 @@ import explicit.gau
 
 fun useSomeClass(): SomeClass = SomeClass()
 
+fun useNested(): SomeClass.Nested = SomeClass.Nested()
+
 fun useAnotherClass(): AnotherClass = AnotherClass()
 
 fun test() {