FPatternPostChangeMovementModeHelper

Silly little bit of indirection to let UPathedPhysicsMovementMode::PostEditChangeChainProperty act like it's a friend of [UPathedMovementPatternBase](API\Plugins\Mover\UPathedMovementPatternBase) without needing to fully declare this class before the pattern (i.e. having PathedMovementPatternBase.h have to include this whole header)