Consistent function naming

[Y-Less]

While these includes originally used lowercase naming, most of the rest of the SA:MP community - including the official includes and major includes and plugins use UpperCase. The naming here is somewhat legacy and should be brought up to date:

#pragma deprecated Use `FuncIDX`.
native funcidx(const name[]);
native FuncIDX(const name[]) = funcidx;

[Shiska]

I see no problem with this but it should be done in a separate branch because we can't know if someone uses one of the uppercase variants as a function name.