Alembic: export render resolution on cameras

Blender's cameras don't have specific resolution configured to them,
instead they use the scene's resolution.
This is a problem when exporting a camera using Alembic. Other software
(like Houdini) expects the resolution parameters on the camera itself.

So now store the scene's resolution on each camera that is exported.
Since this is not part of the concept of a camera in alembic itself,
export these as `userProperties` in a way other software can read this.

Fixes #116375

@@ -47,0 +49,4 @@
+  /* Export scene render resolution on cameras as userProperties, for other software (e.g.
+   * Houdini). */
+  OFloatProperty render_resx(abc_custom_data_container_, "resx");
+  OFloatProperty render_resy(abc_custom_data_container_, "resy");

@@ -47,0 +50,4 @@
+   * Houdini). */
+  OFloatProperty render_resx(abc_custom_data_container_, "resx");
+  OFloatProperty render_resy(abc_custom_data_container_, "resy");
+  Scene *scene = DEG_get_input_scene(args_.depsgraph);