Un-finalize robotToCamera, add getters and setters (#789)

Allows teams with a mechanism that moves the camera's position (eg, a pan and tilt mechanism) to update the location of their camera for their pose calculations.

---------

Co-authored-by: Matthew Morley <matthew.morley.ca@gmail.com>

photon-lib/src/main/native/include/photonlib/PhotonPoseEstimator.h

@@ -123,6 +123,24 @@ class PhotonPoseEstimator {
     this->referencePose = referencePose;
   }
 
+  /**
+   * @return The current transform from the center of the robot to the camera
+   *         mount position.
+   */
+  inline frc::Transform3d GetRobotToCameraTransform() {
+    return m_robotToCamera;
+  }
+
+  /**
+   * Useful for pan and tilt mechanisms, or cameras on turrets
+   *
+   * @param robotToCamera The current transform from the center of the robot to
+   * the camera mount position.
+   */
+  inline void SetRobotToCameraTransform(frc::Transform3d robotToCamera) {
+    m_robotToCamera = robotToCamera;
+  }
+
   /**
    * Update the stored last pose. Useful for setting the initial estimate when
    * using the CLOSEST_TO_LAST_POSE strategy.