Hydra: add option to export through USD file instead of Hydra API

This is currently meant mainly for testing, when "Developer Extras" is
enabled. The goal is to make interactive Hydra export and USD file export
identical. We are not there yet, and having the ability to compare both
in the viewport and automated tests should help us get and stay there.

Ref #110765

scripts/startup/bl_ui/properties_render.py

@@ -1156,6 +1156,25 @@ class RENDER_PT_simplify_greasepencil(RenderButtonsPanel, Panel, GreasePencilSim
     bl_options = {'DEFAULT_CLOSED'}
 
 
+class RENDER_PT_hydra_debug(RenderButtonsPanel, Panel):
+    bl_label = "Hydra Debug"
+    bl_options = {'DEFAULT_CLOSED'}
+    bl_order = 200
+    COMPAT_ENGINES = {'HYDRA_STORM'}
+
+    @classmethod
+    def poll(cls, context):
+        prefs = context.preferences
+        return (context.engine in cls.COMPAT_ENGINES) and prefs.view.show_developer_ui
+
+    def draw(self, context):
+        layout = self.layout
+        layout.use_property_split = True
+
+        hydra = context.scene.hydra
+        layout.prop(hydra, "export_method")
+
+
 classes = (
     RENDER_PT_context,
     RENDER_PT_eevee_sampling,
@@ -1200,6 +1219,7 @@ classes = (
     RENDER_PT_opengl_color,
     RENDER_PT_opengl_options,
     RENDER_PT_opengl_film,
+    RENDER_PT_hydra_debug,
     RENDER_PT_color_management,
     RENDER_PT_color_management_curves,
     RENDER_PT_simplify,