Support cancellation supression of EntityDismount/VehicleExit events"

Entities must be dismounted before teleportation in order to avoid
multiple issues in the server with regards to teleportation, shamefully,
too many plugins rely on the events firing, which means that not firing
these events caues more issues than it solves;

In order to counteract this, Entity dismount/exit vehicle events have
been modified to supress cancellation (and has a method to allow plugins
to check if this has been set), noting that cancellation will be silently
surpressed given that plugins are not expecting this event to not be cancellable.

This is a far from ideal scenario, however: given the current state of this
event and other alternatives causing issues elsewhere, I believe that
this is going to be the best soultion all around.

Improvements/suggestions welcome!

paper-api/src/main/java/org/bukkit/event/entity/EntityDismountEvent.java

@@ -13,10 +13,18 @@ public class EntityDismountEvent extends EntityEvent implements Cancellable {
     private static final HandlerList handlers = new HandlerList();
     private boolean cancelled;
     private final Entity dismounted;
+    private final boolean isCancellable; // Paper
 
     public EntityDismountEvent(@NotNull Entity what, @NotNull Entity dismounted) {
+        // Paper start
+        this(what, dismounted, true);
+    }
+
+    public EntityDismountEvent(@NotNull Entity what, @NotNull Entity dismounted, boolean isCancellable) {
+        // Paper end
         super(what);
         this.dismounted = dismounted;
+        this.isCancellable = isCancellable; // Paper
     }
 
     /**
@@ -36,9 +44,18 @@ public class EntityDismountEvent extends EntityEvent implements Cancellable {
 
     @Override
     public void setCancelled(boolean cancel) {
+        // Paper start
+        if (cancel && !this.isCancellable) {
+            return;
+        }
         this.cancelled = cancel;
     }
 
+    public boolean isCancellable() {
+        return this.isCancellable;
+        // Paper end
+    }
+
     @NotNull
     @Override
     public HandlerList getHandlers() {

paper-api/src/main/java/org/bukkit/event/vehicle/VehicleExitEvent.java

@@ -13,10 +13,18 @@ public class VehicleExitEvent extends VehicleEvent implements Cancellable {
     private static final HandlerList handlers = new HandlerList();
     private boolean cancelled;
     private final LivingEntity exited;
+    private final boolean isCancellable; // Paper
 
-    public VehicleExitEvent(@NotNull final Vehicle vehicle, @NotNull final LivingEntity exited) {
+    public VehicleExitEvent(@NotNull final Vehicle vehicle, @NotNull final LivingEntity exited, boolean isCancellable) { // Paper
         super(vehicle);
         this.exited = exited;
+        // Paper start
+        this.isCancellable = isCancellable;
+    }
+
+    public VehicleExitEvent(@NotNull final Vehicle vehicle, @NotNull final LivingEntity exited) {
+        this(vehicle, exited, true);
+        // Paper end
     }
 
     /**
@@ -36,9 +44,18 @@ public class VehicleExitEvent extends VehicleEvent implements Cancellable {
 
     @Override
     public void setCancelled(boolean cancel) {
+        // Paper start
+        if (cancel && !isCancellable) {
+            return;
+        }
         this.cancelled = cancel;
     }
 
+    public boolean isCancellable() {
+        return isCancellable;
+        // Paper end
+    }
+
     @NotNull
     @Override
     public HandlerList getHandlers() {