Report GBA game as inserted in the second slot to the DS game

[RodrigoTR04]

Is your feature request related to a problem? Please describe.

Feature being requested is not for a problem, it is for DS games to be able to know if there is a GBA game inserted in the second slot.

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Describe the solution you'd like

Select a GBA ROM file in the SD/microSD card to be understood as being inserted into the second slot as if it were in a DS Phat/Lite, but without being forced to stick to them, being able to emulate that in a DSi or 3DS running a DS game for example.

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Describe alternatives you've considered

Not applicable

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Additional context

Some games like Pokemon Diamond, Pearl and Platinum offer some exclusive encounters in-game if certain GBA games are inserted into the second slot, currently that's only possible with a DS Phat/Lite, playing them in a DSi or 3DS does not allow for those encounters to be done.
Here's a link for context: https://bulbapedia.bulbagarden.net/wiki/Dual-slot_mode

Note: this is not asking for a way to transfer Pokemon from generation 3 to generation 4, for that there is already PKSM (a save manager) that does the job, this is purely for the in-game encounters.