What is build into the VCL is the drag and dock support also used by the RAD Studio IDE, the "snap to border" functionality is something different. If none of these two features match your need you have to build you own, which you seem to have done now.
Do you know you can use inheritance with forms as well? Build a base form class with the functionality you need, add it to any new project you need this functionality in and then create new forms in the designer by using File -> New -> Others, and pick the base class from the "inheritable items" section. Just changing the ancestor class from TFrom to your base class in the editor does not work directly, since forms have associated DFM files. You would also need to edit the DFM file as text and change the first "object" to "inherited" for this to work.