[RCORE] Make some config defines settable by build systems

[JeffM2501]

The way config.h and it's 'SUPPORT_FEATURE' flags are setup right now makes it impossible for build systems to change these flags without fully redefining every feature in config.h. This is not easy for people to do, and is counter to raylib's simple design.

This PR takes 3 of those flags and reverses the sense of them, turning them from SUPPORT_ flags to DISABLE_ flags.

• Screen Capture
• GIF recording
• High Resolution Timer

This means that by default raylib will enable the code that implements these features, unless the build system defines the specific DISABLE_ feature flag.

By reversing these defines, it makes it very easy for people to simply add the things they want to turn off to a makefile or project. Raylib has gone from 'add stuff to it' to 'remove stuff you don't need from it'.

I simply picked 3 flags that made the most sense to disable, if this concept is accepted we can apply it additional features.
The big ones here are screen capture and gif recording since they use a specific key that people may want to use for other features (this is my use case)

[raysan5]

@JeffM2501 I'm afraid this change breaks consistency. I prefer to look for a more consistent solution to this issue, probably following discussion here #4411

[JeffM2501]

I was unaware of that issue, I will make a PR that does that. I have a need to be able to disable features.
The solution in that PR works for me, we just need to do something.