Gui: Use getObject<T>() helpers in classes

This commit is generated using regex based find and replace:

```
s/[\w:]+_cast\s*<([^>]+)\*>\s*\(\s*getObject\(\s*\)\)/getObject<$1>/
s/[\w:]+_cast\s*<([^>]+)\*>\s*\(\s*([^)]*)\s*->\s*getObject\(\s*\)\)/$2->getObject<$1>()/
```

To regenerate if needed.

src/Mod/Spreadsheet/Gui/ViewProviderSpreadsheet.cpp

@@ -111,7 +111,7 @@ void ViewProviderSheet::showSheetMdi()
 
 void ViewProviderSheet::exportAsFile()
 {
-    auto* sheet = static_cast<Spreadsheet::Sheet*>(getObject());
+    auto* sheet = getObject<Spreadsheet::Sheet>();
     QString selectedFilter;
     QString formatList = QObject::tr("CSV (*.csv *.CSV);;All (*)");
     QString fileName = Gui::FileDialog::getSaveFileName(Gui::getMainWindow(),