Core: Fixed a bug where an empty document disappears (#20554)

* Core: Fixed a bug where an empty document disappears

Created a flag named autoCreated to distinguish an autoCreated
document created in the startup from a manually document.
Implemented a setter and a getter for this new flag.
Added a codition that verifies if a document is autoCreated
when opening another document to close it in the correct case.
Implemented unit tests for theses cases. Fixes #19868.

Signed-off-by: João Neves <joao.antonio.neves@tecnico.ulisboa.pt>

* Tests: Fix failing auto-created document tests

Signed-off-by: João Neves <joao.antonio.neves@tecnico.ulisboa.pt>

* Tests: moved created tests to the existing Document test framework.

Signed-off-by: João Neves <joao.antonio.neves@tecnico.ulisboa.pt>

---------

Signed-off-by: João Neves <joao.antonio.neves@tecnico.ulisboa.pt>

src/Gui/MainWindow.cpp

@@ -1564,6 +1564,9 @@ void MainWindow::delayedStartup()
     if (hGrp->GetBool("CreateNewDoc", false)) {
         if (App::GetApplication().getDocuments().empty()){
             Application::Instance->commandManager().runCommandByName("Std_New");
+            // This document is autoCreated
+            App::Document* newDoc = App::GetApplication().getActiveDocument();
+            newDoc->setAutoCreated(true);
         }
     }