Key split restructure (#2168)

Key split tables have been given names based on usage (KeySplitTable1 -> keysplit_piano etc) and a new macro has been set up to better represent the individual bytes for key splits with it being more obvious to how said bytes are used for the respective voice in the voicegroup.

---------

Co-authored-by: Martin Griffin <[email protected]>

Author: ShinyDragonHunter

asm/macros/m4a.inc

@@ -21,3 +21,31 @@
 		.set voicegroup_\label, . - \starting_note * 0xC
 	.endif
 	.endm
+
+	.macro keysplit label:req, starting_note
+	.ifb \starting_note
+		.global keysplit_\label
+		keysplit_\label:
+		.set _last_note, 0
+	.else
+		.set keysplit_\label, . - \starting_note
+		.set _last_note, \starting_note
+	.endif
+	.set _last_split, 0
+	.endm
+
+	.macro split index:req, ending_note:req
+	.if \ending_note < _last_note
+		.if _last_split == 0
+			.error "split's ending_note earlier than previous keysplit's starting_note"
+		.else
+			.error "split's ending_note earlier than previous split's ending_note"
+		.endif
+	.else
+	.rept \ending_note - _last_note
+	  .byte \index
+	.endr
+	.endif
+	.set _last_note, \ending_note
+	.set _last_split, 1
+	.endm