widget overlay: Don't draw empty wilderness K/D box

The Wilderness and PVP kill-death information box is created while in
these areas regardless of whether the setting (configured via the notice
board at the Edgeville bank) is enabled to show the text, meaning the
widget contains only empty text widgets when the setting is disabled
rather than being null, causing a bounding box to still be drawn and
affecting other snapped widget layout. This commit adds a child class of
WidgetOverlay specific to this widget and prevents it from being drawn
when the setting to show this information is disabled.

runelite-api/src/main/java/net/runelite/api/Varbits.java

@@ -639,7 +639,16 @@ public enum Varbits
 	 * 0 = on
 	 * 1 = off
 	 */
-	BOSS_HEALTH_OVERLAY(12389);
+	BOSS_HEALTH_OVERLAY(12389),
+
+	/**
+	 * Whether the PVP kill-death stats widget should be drawn while in the wilderness or in PVP worlds.
+	 *
+	 * 0 = Disabled
+	 * 1 = Enabled
+	 */
+	SHOW_PVP_KDR_STATS(4143),
+	;
 
 	/**
 	 * The raw varbit ID.