Utilze "folder merging" with SCU

[dustdfg]

Current scu implementation has internal ability to merge code from folders (subfolders to be more precise) but it isn't used in the code at all... We are passing arrays of individual folders while could leverage merging of those folders by passing arrays with several folders. The function is made for this... It would increase possibility of namespace collisions and etc but in some places it is reasonable enough I think...

    process_folder(["editor/gui"])
    process_folder(["editor/inspector"], ["editor_resource_preview"])
    process_folder(["editor/themes"])
    process_folder(["editor/project_manager"])
    process_folder(["editor/project_upgrade"])
    process_folder(["editor/import"])
    process_folder(["editor/import/3d"])
    process_folder(["editor/plugins"])
    process_folder(["editor/run"])
    process_folder(["editor/scene"])
    process_folder(["editor/scene/2d"])
    process_folder(["editor/scene/2d/physics"])
    process_folder(["editor/scene/2d/tiles"])
    process_folder(["editor/scene/3d"])
    process_folder(["editor/scene/3d/gizmos"])
    process_folder(["editor/scene/gui"])
    process_folder(["editor/scene/texture"])
    process_folder(["editor/script"])

Additionally as example after PR to split editor folder it also split ability to make big SCU files

@lawnjelly