All the driver-specific code in `fcurve.c` has been moved into a new file `fcurve_driver.c`. The corresponding declarations have been moved from `BKE_fcurve.h` to `BKE_fcurve_driver.h`. All the `#include "BKE_fcurve.h"` statements have been investigated and replaced with `BKE_fcurve_driver.h` where necessary. No functional changes.