Add a warning if Seat:Sit() is called from the client

[galmeowing (Quaywinn)]

Based on the bug report for Seat:Sit() having a lot of traction, there should be a warning for this so developers don’t run into undefined behaviour and not know that calling Seat:Sit() from the client can lead to undefined behavior

Seat:Sit() does not consistently work from client

Hello! Apologies this was never resolved. Ultimately, this seems like the anticipated behavior - Seat:Sit is designed to be called on the Server, not the Client, as it creates a weld between the character and the seat. This must happen on the Server in order to maintain a consistent world across the server and all the clients. In general, welds that are created locally are not replicated to the server/other clients. If a weld is created on the Client, it can de-sync from the Server, resulting in…