9a3abe22a3
This is part of #121565. Refactors `legacy_gpencil_to_grease_pencil` to use `GreasePencil::insert_frame` instead of manually creating the drawing array. Now `legacy_gpencil_frame_to_grease_pencil_drawing` actually returns a drawing by value. Note: This means that we're now resizing the drawing array for every frame in every layer, but this can be optimized later.