Only expose velocity relative tp flags to API (#11532)

Since 1.21.2, vanilla split relative teleportation flags into position
and delta/velocity flags into separate enum entries.
This highlighted a design flaw in the paper api addition for teleport
flags, which just simply mirrored internals while also only being able
to apply the delta/velocity part of a flag, given the teleport target is
always absolute in the API.

This patch proposes to simply no longer expose the non-velocity related
flags to the API, instead marking the entire Relative enum as being
purely velocity related, as non-velocity related flags are not useful to
callers. This was done over simply exposing all internal flags, as
another vanilla change to the internal enum would result in the same
breakage.

The newly proposed API *only* promises that the passed flags prevent the
loss of velocity in the specific axis/context, which should be
independent enough of vanillas specific implementation of this feature.

patches/server/0884-Add-player-idle-duration-API.patch

@@ -6,10 +6,10 @@ Subject: [PATCH] Add player idle duration API
 Implements API for getting and resetting a player's idle duration.
 
 diff --git a/src/main/java/org/bukkit/craftbukkit/entity/CraftPlayer.java b/src/main/java/org/bukkit/craftbukkit/entity/CraftPlayer.java
-index 96d8bd55ecfb6aca8a6f65bc2a25e5756eecc4d8..fee7f60d457f34dd46756efc51bf21bd5498d854 100644
+index de97ca0a25d70de50dfcc6b092f5e58facfb5a3a..b4f967c8cc0800d0606e7ad32ff8a350387c6132 100644
 --- a/src/main/java/org/bukkit/craftbukkit/entity/CraftPlayer.java
 +++ b/src/main/java/org/bukkit/craftbukkit/entity/CraftPlayer.java
-@@ -3443,6 +3443,18 @@ public class CraftPlayer extends CraftHumanEntity implements Player {
+@@ -3441,6 +3441,18 @@ public class CraftPlayer extends CraftHumanEntity implements Player {
      }
      // Paper end