Simplify SGB related UIs and make it possible to use SGB under Gambatte link

[Fortranm]

This is a revision of #3283 made to work on BizHawk 2.9.

https://en.wikipedia.org/wiki/Super_Game_Boy#Super_Game_Boy_2

The Super Game Boy 2 was released exclusively in Japan in 1998. Additions included a link port to allow a user to access two-player mode via the link cable...

Currently, the SGB mode of Gambatte has to be turned on via Config > Cores > GB in SGB instead of in the sync setting and cannot be used in GB Link as a result.

This PR does three things related to SGB:

1. SGB is added (or rather, merged in) as a Console Mode option for Gambatte.
   

2. "GB in SGB" check box and SGB core picker are removed and the BSNES cores are added under the GB core picket (legacy BSNES core not included). GB/GBC games will load under SGB mode of the corresponding BSNES core if one of those options are chosen.
   

3. As a result of the first change (with addition adjustments), it is now possible to use SGB mode in Gambatte Link too.
   
   
   
   
   Each SGB core can have up to 4 controllers linked to it. The Power button for each SGB core is included on the first Player tab of the core for the time being.
   Note that the tab parsing process is currently hardcoded to categorize every item that starts with "Px " under the tab "Player x" and everything else under "Console". There have been suggestions to use "Console x" for a core in link mode but that requires enough refactoring to be considered a separate task IMO.

Note: The SGB sound is not implemented yet but that can be done along with the MBC sound fix for Gambatte Link altogether later.

[TiKevin83]

approving from a code perspective, haven't done a QA of the functionality yet

[Morilli]

Haven't tested the gambatte changes extensively but I think this is solid enough to get in. The "gb as sgb" UX flow was pretty bad imo so this is a definite improvement.

[YoshiRulz]

I'm curious of what @CasualPokePlayer has to say, specifically about the video buffer stuff. But this now LGTM in terms of code. (I think you deserve some kind of trophy for hacking together the button mapping by doing it in the wrong direction and with 3 nested loops.)
As for functionality, opening a 4x bundle and immediately closing it results in:

stacktrace

System.NullReferenceException: Object reference not set to an instance of an object
  at BizHawk.Emulation.Common.LinkedSaveRam.CloneSaveRam () [0x0002f] in <f3a4da15026e4f05ab7072e9a135677c>:0
  at BizHawk.Client.EmuHawk.MainForm.FlushSaveRAM (System.Boolean autosave) [0x000f0] in <5e7f3991f9b246bb80e8d9725eda76e1>:0
  at (wrapper remoting-invoke-with-check) BizHawk.Client.EmuHawk.MainForm.FlushSaveRAM(bool)
  at BizHawk.Client.EmuHawk.MainForm.CloseGame (System.Boolean clearSram) [0x0006f] in <5e7f3991f9b246bb80e8d9725eda76e1>:0
  at BizHawk.Client.EmuHawk.MainForm.CloseRom (System.Boolean clearSram) [0x00010] in <5e7f3991f9b246bb80e8d9725eda76e1>:0
  at (wrapper remoting-invoke-with-check) BizHawk.Client.EmuHawk.MainForm.CloseRom(bool)
  at BizHawk.Client.EmuHawk.MainForm.CheckHotkey (System.String trigger) [0x01588] in <5e7f3991f9b246bb80e8d9725eda76e1>:0
  at BizHawk.Client.EmuHawk.MainForm.<ProcessInput>b__143_0 (System.Boolean current, System.String trigger) [0x00000] in <5e7f3991f9b246bb80e8d9725eda76e1>:0
  at System.Linq.Enumerable.Aggregate[TSource,TAccumulate] (System.Collections.Generic.IEnumerable`1[T] source, TAccumulate seed, System.Func`3[T1,T2,TResult] func) [0x0002e] in <89a8dc5bc33447a4a98f23a2d52e8aee>:0
  at BizHawk.Client.EmuHawk.MainForm.ProcessInput (BizHawk.Client.Common.InputCoalescer hotkeyCoalescer, BizHawk.Client.Common.ControllerInputCoalescer finalHostController, System.Func`2[T,TResult] searchHotkeyBindings, System.Func`2[T,TResult] activeControllerHasBinding) [0x00135] in <5e7f3991f9b246bb80e8d9725eda76e1>:0
  at BizHawk.Client.EmuHawk.MainForm.ProgramRunLoop () [0x0009c] in <5e7f3991f9b246bb80e8d9725eda76e1>:0
  at (wrapper remoting-invoke-with-check) BizHawk.Client.EmuHawk.MainForm.ProgramRunLoop()
  at BizHawk.Client.EmuHawk.Program.SubMain (System.String[] args) [0x0042b] in <5e7f3991f9b246bb80e8d9725eda76e1>:0

[Morilli]

As for functionality, opening a 4x bundle and immediately closing it results in: [System.NullReferenceException]

fwiw I cannot reproduce that exception when testing with either GambatteLink or GBHawk4x as everything seems to work and play and close just fine. Do you have a specific bundle that shows this issue?

[YoshiRulz]

4x Chikyū Kaihō Gun ZAS SHA1:2FF6D0242D845669445E3D97FFFAE5C5F7943CFD in a bundle and the crash is immediate, not on close. The rom on its own is fine in Gambatte. This is on 9ee3830 under Mono. I suspect it has something to do with the mapper, because 4x Pokemon Yellow is fine. I kept testing and it's apparently the name in the bundle which determines whether or not it's crashing? I'll clean build and check again.

[YoshiRulz]

I still don't have a nice repro, but I found the culprit with print-debugging, and it wasn't related to this PR. I'll push a fix to master later.
In working on that, I've seen that SGB in GambatteLink is working, so I won't block this any further. @CasualPokePlayer?