[SETUPLIB][USETUP] Don't store UI-related display strings in GENERIC_LIST_ENTRY-ies, + other code adaptations.

- Apart from allowing a UI cache variable that may be used when
  displaying GENERIC_LIST_ENTRY-ies, do not store any display strings
  associated to these list entries. They should be instead computed only
  when initializing a list UI (or a combo-box or list control if the
  code is used in Win32 environment).
  For this matter a callback is provided to InitGenericListUi() that
  does the job of computing the displayed string corresponding to a
  given GENERIC_LIST_ENTRY.

- Simplify the calls to InitGenericListUi(), and refactor the
  RestoreGenericListUiState() function.

- Use for-loops for iterating over GENERIC_LIST items.

- Adapt the storage data format for lists of settings items.

- The txtsetup.sif INF format specified in LoadSetupInf() should not be
  INF_STYLE_WIN4 (to be investigated...).

base/setup/lib/setuplib.c

@@ -516,7 +516,7 @@ LoadSetupInf(
 
     *SetupInf = SetupOpenInfFileExW(FileNameBuffer,
                                    NULL,
-                                   INF_STYLE_WIN4 | INF_STYLE_OLDNT,
+                                   /* INF_STYLE_WIN4 | */ INF_STYLE_OLDNT,
                                    pSetupData->LanguageId,
                                    &ErrorLine);