Fix get_scene_tile_display_placeholder erroring for transformed scene tiles

[kleonc]

Makes TileSetScenesCollectionSource::get_scene_tile_display_placeholder ignore transform bits encoded within the passed alternative id, just like it's done in TileSetScenesCollectionSource::get_scene_tile_scene:

godot/scene/resources/2d/tile_set.cpp

Lines 5852 to 5855 in d743736

	bool TileSetScenesCollectionSource::get_scene_tile_display_placeholder(int p_id) const {
	ERR_FAIL_COND_V(!scenes.has(p_id), false);
	return scenes[p_id].display_placeholder;
	}

godot/scene/resources/2d/tile_set.cpp

Lines 5838 to 5842 in d743736

	Ref<PackedScene> TileSetScenesCollectionSource::get_scene_tile_scene(int p_id) const {
	int scene_tile = TileSetAtlasSource::alternative_no_transform(p_id);
	ERR_FAIL_COND_V(!scenes.has(scene_tile), Ref<PackedScene>());
	return scenes[scene_tile].scene;
	}

It was making e.g. placing transformed scene tiles spam errors.

Before (v4.6.dev6.official [dec5a37]):

Godot_v4.6-dev6_win64_9EsGjZTyG1.mp4

After (this PR):

godot.windows.editor.dev.x86_64_3ejjzzaWsZ.mp4

[Repiteo]

Thanks!