Fix setting passengers performs mount logic (#3565)

Fixes #3492
Fixes #3493

Author: aromaa

src/accessors/java/org/spongepowered/common/accessor/world/entity/EntityAccessor.java

@@ -91,8 +91,6 @@ public interface EntityAccessor {
 
     @Accessor("portalEntrancePos") void accessor$portalEntrancePos(final BlockPos portalEntrancePos);
 
-    @Accessor("passengers") List<Entity> accessor$passengers();
-
     @Invoker("setRot") void invoker$setRot(final float yRot, final float xRot);
 
     @Invoker("getEncodeId") @Nullable String invoker$getEncodeId();

src/main/java/org/spongepowered/common/data/provider/entity/EntityData.java

@@ -169,8 +169,8 @@ public static void register(final DataProviderRegistrator registrator) {
                     .create(Keys.PASSENGERS)
                         .get(h -> h.getPassengers().stream().map(org.spongepowered.api.entity.Entity.class::cast).collect(Collectors.toList()))
                         .set((h, v) -> {
-                            ((EntityAccessor) h).accessor$passengers().clear();
-                            v.forEach(v1 -> ((EntityAccessor) h).accessor$passengers().add((Entity) v1));
+                            h.ejectPassengers();
+                            v.forEach(v1 -> ((Entity) v1).startRiding(h, true));
                         })
                     .create(Keys.REMAINING_AIR)
                         .get(h -> Math.max(0, h.getAirSupply()))