[LL FIR] StubBasedFirDeserializedSymbolProvider: fix loading of nested classes

We cannot load nested class without an outer as in this case we will
miss a symbol of the outer class, which is crucial in some cases
(e.g., during status calculation).
So we have to load the topmost class as it will load all nested classes
with the correct context as well

^KT-62891 Fixed

analysis/analysis-api/testData/components/diagnosticsProvider/diagnostics/overrideProtectedClassReturnFromLibrary.standalone.fir.txt

@@ -1 +0,0 @@
-Diagnostics from elements:

analysis/analysis-api/testData/components/diagnosticsProvider/diagnostics/overrideProtectedClassReturnFromLibrary.txt

@@ -1,4 +1 @@
 Diagnostics from elements:
-  for PSI element of type KtNamedFunction at (15,5-64)
-    EXPOSED_FUNCTION_RETURN_TYPE      text ranges: [(103,123)]
-      PSI: KtNamedFunction at (15,5-64)