how to design AC line filter for VFD?
It will be impossible to remove the harmonics and difficult to reduce the harmonic content to a negligible level. You should determine what level is acceptable. Putting an AC reactor in the AC line or a DC reactor after the bridge may be sufficient. Many low-power VFDs on the market have very little built-in harmonic current mitigation. A VFD for a single-phase induction motor would be considered low-power.