api: replace varbits enum with ints

This adds a Varbit magic constant annotation which is used now on
varbit parameters and fields.

This is roughly the same type-safety wise, with IDE support, but the ids
can be inlined by the compiler and it avoids having to have a large enum
class with many fields.

runelite-api/pom.xml

@@ -120,6 +120,7 @@
 								<exclude>net/runelite/api/SoundEffectVolume.class</exclude>
 								<exclude>net/runelite/api/SpriteID.class</exclude>
 								<exclude>net/runelite/api/StructID.class</exclude>
+								<exclude>net/runelite/api/Varbits.class</exclude>
 							</excludes>
 						</configuration>
 					</execution>