[WIP] CVar rework

[Rozelette]

This is a WIP example of reworking CVars to solve several issues with them. This is the SoH side of things, for the LUS PR, see Kenix3/libultraship#137.

The issues I am trying to fix:

• CVar lookup is expensive since it involves a map lookup. It is one of the most expensive things that occurs in the game update loop (so outside of graphics/rendering)
• CVar usage is error-prone. Since they are identified with strings, and defaulted if they don't exist (a common occurrence since they don't exist until they are changed), there is potential for misspellings to result in bugs that go undetected.

The changes needed in SoH are less structural, and more just needed as a client of the new interface. They do present an example of the intended interface. This PR reworks the values previously held in global.sav to be the new version of CVars. As such, they no longer need to be saved, since they will be saved with the CVars. Let's see what was needed to convert them.

• There are new files, GlobalSettings.h/.cpp and z64settings.h
• z64settings.h contains a global struct of settings that exist outside of any file-specific data. Data was moved out from gSaveContext accordingly.
• GlobalSettings is the C++ side of things and manages defaulting and associating the data with CVars.

So, to add a new setting and associated CVar you:

• Add data to the struct in z64settings.h
• Add the default in GlobalSettings.cpp
• Add the CVar also in GlobalSettings.cpp

That's it! Now you can use it just like a regular C variable and it'll get saved along with all the other CVars.

Update: made a second commit to show how to convert the existing usage into the new usage.

[Rozelette]

As a note, this is a bug caught by the checks I added in the new CVars system. The default value was a pointer, instead of 0 (false) that it was everywhere else.

[dcvz]

I've gone through this @Rozelette! I started here (and have not checked LUS) because when designing new systems I think its most important what it feels like to the user.

I really love the concept of everything just being vars that you can use in code and not having to worry about fetching and default values at the usage point.

One thing that I wonder if can be improved is that it's a 3 step process to make a new var. You add it to some struct, you register the default value for that property and then you register it as a Cvar (being persistable) if it needs to be persisted.

I wonder if there's any way we can achieve that with just one structure? Perhaps code generation? Perhaps a macro? Given that we're working in C-land that may not be possible but wanted to get gears turning.

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It might not be possible but it would be great to be able to do something like:

// key that will be used, type, default value, persisted
CreateVar("global.language", s32, LANGUAGE_ENG, true);
CreateVar("global.zTargetSetting", s32, 0, false);

which maybe generates:

typedef struct {
   s32 language;
   s32 zTargetSetting;
} global;

global.language = LANGUAGE_ENG;
global.zTargetSetting = 0;

cvar->RegisterManaged("gLanguage", global.language);

[aMannus]

Going to close this for now. Feel free to open a new PR whenever it's further ahead.