Add meaningful aliases for wd265

Introduce MONICON_* constants
Introduce BATTLEPLAYERACTION_* constants

constants/icon_constants.asm

@@ -39,3 +39,13 @@
 	const ICON_SLOWPOKE
 	const ICON_SUDOWOODO
 	const ICON_BIGMON
+
+; LoadMenuMonIcon.Jumptable indexes (see engine/gfx/mon_icons.asm)
+	const_def
+	const MONICON_PARTYMENU
+	const MONICON_NAMINGSCREEN
+	const MONICON_MOVES
+	const MONICON_TRADE
+	const MONICON_MOBILE1
+	const MONICON_MOBILE2
+	const MONICON_UNUSED