Make prefab system enabled as default for automated tests (#5670)

* Make prefab system enabled as default for automated tests

Signed-off-by: chiyenteng <82238204+chiyenteng@users.noreply.github.com>

* Modify auto tests after preventing regset saved into disk after editor main window closed

Signed-off-by: chiyenteng <82238204+chiyenteng@users.noreply.github.com>

* Uncomment xfail

Signed-off-by: chiyenteng <82238204+chiyenteng@users.noreply.github.com>

* Use --regset for editor tests

Signed-off-by: chiyenteng <82238204+chiyenteng@users.noreply.github.com>

Tools/LyTestTools/ly_test_tools/o3de/editor_test.py

@@ -303,6 +303,8 @@ class EditorTestSuite():
     use_null_renderer = True
     # Maximum time for a single editor to stay open on a shared test
     timeout_editor_shared_test = 300
+    # Flag to determine whether to use new prefab system or use deprecated slice system for this test suite
+    enable_prefab_system = True
 
     # Function to calculate number of editors to run in parallel, this can be overriden by the user
     @staticmethod
@@ -741,7 +743,11 @@ class EditorTestSuite():
             test_cmdline_args += ["--attach-debugger"]
         if test_spec.wait_for_debugger:
             test_cmdline_args += ["--wait-for-debugger"]
-            
+        if self.enable_prefab_system:
+            test_cmdline_args += ["--regset=/Amazon/Preferences/EnablePrefabSystem=true"]
+        else:
+            test_cmdline_args += ["--regset=/Amazon/Preferences/EnablePrefabSystem=false"]
+
         # Cycle any old crash report in case it wasn't cycled properly
         editor_utils.cycle_crash_report(run_id, workspace)
 
@@ -804,7 +810,11 @@ class EditorTestSuite():
             test_cmdline_args += ["--attach-debugger"]
         if any([t.wait_for_debugger for t in test_spec_list]):
             test_cmdline_args += ["--wait-for-debugger"]
-            
+        if self.enable_prefab_system:
+            test_cmdline_args += ["--regset=/Amazon/Preferences/EnablePrefabSystem=true"]
+        else:
+            test_cmdline_args += ["--regset=/Amazon/Preferences/EnablePrefabSystem=false"]
+
         # Cycle any old crash report in case it wasn't cycled properly
         editor_utils.cycle_crash_report(run_id, workspace)