Deduplicate settings/syncsettings of linked (2x/3x/4x) cores

The hard part here is the autogenerated UI.

edit: GGHawkLink => SMSHawk mmmkay?

My suggestion is to use one instance of the non-link-core type per console (e.g. 2x GBHawk.GBSyncSettings instead of 1x GBHawkLink.GBLinkSyncSettings), and to set the props which apply to all consoles on all instances when saving from the UI. (And reading from the first when loading the UI.)

The UI generation code can differentiate per-console props with just one new attribute, either:

[SplitPerLinkedConsole] public GBHawk.GBHawk.GBSyncSettings.ConsoleModeType ConsoleMode { get; set; }
public bool GBACGB { get; set; }

or:

public GBHawk.GBHawk.GBSyncSettings.ConsoleModeType ConsoleMode { get; set; }
[SharedForLinkedConsoles] public bool GBACGB { get; set; }

where the current code looks like:

public GBHawk.GBHawk.GBSyncSettings.ConsoleModeType ConsoleMode_L { get; set; }
public GBHawk.GBHawk.GBSyncSettings.ConsoleModeType ConsoleMode_R { get; set; }
public bool GBACGB { get; set; }

Start with the autogenerated UI and the linked-core settings/syncsettings described in the issue, comparing the per-console and shared properties. Done means linked cores use one non-link-core settings instance per console, shared properties save to and load from the appropriate instances, and per-console properties remain distinct.