The Healgun is a cut gadget that was to appear in Battlefield 2142. It is only referenced in the localization strings, and no other trace of it can be found within the game files.
The Healgun was originally intended to replace the Medkit. It was meant to shoot medicinal darts at players to heal them, but internal testing indicated it was very difficult to use for players as the darts often missed. The deployable Medkit made the cut instead. The model and texture for the Healgun can be seen in the Player Abilities Sprintcor 20 Enhanced Endurance and Staminar 9 Recovery System.