Use `RUNION` macros for overlapping `_RS` constants

[Rangi42]

We use the _RS constants rb/rw for defining struct offsets, like for base data struct members. However, some of these members overlap. Currently we manually reset the _RS value and continue:

DEF BASE_TYPES       rw
rsset BASE_TYPES
DEF BASE_TYPE_1      rb
DEF BASE_TYPE_2      rb

DEF MON_CAUGHTDATA         rw
rsset MON_CAUGHTDATA
DEF MON_CAUGHTTIME         rb
DEF MON_CAUGHTGENDER       rb
rsset MON_CAUGHTDATA
DEF MON_CAUGHTLEVEL        rb
DEF MON_CAUGHTLOCATION     rb

I think it would be cleaner to define RUNION macros (inspired by the WLA-DX assembler's and .UNION-inside-.ENUM feature): https://pastebin.com/7uakxqb6

runion
DEF BASE_TYPES       rw
nextru
DEF BASE_TYPE_1      rb
DEF BASE_TYPE_2      rb
endrunion

runion
DEF MON_CAUGHTDATA         rw
nextru
DEF MON_CAUGHTTIME         rb
DEF MON_CAUGHTGENDER       rb
nextru
DEF MON_CAUGHTLEVEL        rb
DEF MON_CAUGHTLOCATION     rb
endrunion

[vulcandth]

I think the use of unions here make it easier to understand the size of the overlapping constants.

Also to hijack the thread, thoughts on indenting the unions? Although since we normally use tabs for indention and DEF's are normally on column 0.. it makes it look a bit weird.

rsreset
DEF MON_SPECIES                rb
DEF MON_ITEM                   rb
DEF MON_MOVES                  rb NUM_MOVES
DEF MON_OT_ID                  rw
DEF MON_EXP                    rb 3
	runion
	DEF MON_STAT_EXP       rw NUM_EXP_STATS
	nextru
	DEF MON_HP_EXP         rw
	DEF MON_ATK_EXP        rw
	DEF MON_DEF_EXP        rw
	DEF MON_SPD_EXP        rw
	DEF MON_SPC_EXP        rw
	endrunion
DEF MON_DVS                    rw
DEF MON_PP                     rb NUM_MOVES
DEF MON_HAPPINESS              rb
DEF MON_POKERUS                rb
	runion
	DEF MON_CAUGHTDATA     rw
	nextru
	DEF MON_CAUGHTTIME     rb
	DEF MON_CAUGHTGENDER   rb
	nextru
	DEF MON_CAUGHTLEVEL    rb
	DEF MON_CAUGHTLOCATION rb
	endrunion
DEF MON_LEVEL                  rb
DEF BOXMON_STRUCT_LENGTH EQU _RS
DEF MON_STATUS                 rb
                               rb_skip
DEF MON_HP                     rw
DEF MON_MAXHP                  rw
	runion
	DEF MON_STATS          rw NUM_BATTLE_STATS
	nextru
	DEF MON_ATK            rw
	DEF MON_DEF            rw
	DEF MON_SPD            rw
	DEF MON_SAT            rw
	DEF MON_SDF            rw
	endrunion
DEF PARTYMON_STRUCT_LENGTH EQU _RS

[Rangi42]

IMO keep the union keywords unindented, but indenting the DEFs they contain is good (just like in macros).