[apps] Deal with aliases in PointCloud Editor app

After #3753, the PointCloud Editor app has mixed references to pcl::shared_ptr and std::shared_ptr due to the existence of the file localTypes.h. I believe the best course of action would be to remove:

https://github.com/PointCloudLibrary/pcl/blob/336f1927276731b323e22addf6356fc1d6cd0fb4/apps/point_cloud_editor/include/pcl/apps/point_cloud_editor/localTypes.h#L69-L91

and

https://github.com/PointCloudLibrary/pcl/blob/336f1927276731b323e22addf6356fc1d6cd0fb4/apps/point_cloud_editor/include/pcl/apps/point_cloud_editor/localTypes.h#L100-L102

from the file and deal with the ruckus of every other file using that one in the app. This means using the same strategy of the referenced PR and introducing in-class aliases like e.g.:

class Cloud : public Statistics
{
  public:
    /// The type for shared pointer pointing to a selection buffer
    using SelectionPtr = pcl::shared_ptr<Selection>;

    [...]
};

Start with apps/point_cloud_editor/include/pcl/apps/point_cloud_editor/localTypes.h, inspect the aliases at the referenced lines, and search the PointCloud Editor app for their users. Replace the shared-pointer aliases using the in-class approach described in the issue, then build the app and confirm the mixed alias references are gone.