This does not actually add SDL3 support but adds enough
CMake stuff to make the following succeed:
```bash
cmake -S. -Bbuild-sdl3 -DUSE_SDL3=ON -DDEVILUTIONX_SYSTEM_SDL3=OFF -DDEVILUTIONX_STATIC_SDL3=ON -DNOSOUND=ON
```
`NOSOUND` is needed because `SDL_audiolib` does not support SDL3.
Now that the DOS SDL supports CMake, this is a much better option that
`configure`, because it lets us easily test out local changes to SDL,
e.g.:
```bash
cmake -S. -Bbuild-dos -DCMAKE_TOOLCHAIN_FILE=CMake/platforms/djcpp.toolchain.cmake \
-DTARGET_PLATFORM="dos" -DCMAKE_BUILD_TYPE=Release -DBUILD_TESTING=OFF \
-DFETCHCONTENT_SOURCE_DIR_SDL2="${HOME}/diasurgical-SDL"
```
Also renames lua/lua.hpp to lua/lua_global.hpp.
The previous name broke version auto-detection in sol2, which involves
calling `__has_include(<lua/lua.hpp>)`.
On CMake v3.28+, `EXCLUDE_FROM_ALL` is supported natively as an argument
to `FetchContent_Declare`.
On CMake v3.30+, `FetchContent_Populate`, which we use to polyfill
`EXCLUDE_FROM_ALL` support for older versions of CMake, is deprecated
and triggers a noisy warning.
Avoids the warning by using the native `EXCLUDE_FROM_ALL` support on
CMake v3.28+.
Our implementation has a more modern interface and only
supports the features that we care about.
It always outputs `\n` as newlines and does not output BOM.
The modern interface eliminates awkward `c_str()/data()` conversions.
This implementation preserves comments and the file order of sections
and keys. New keys are written in insertion order.
We now also support modifying and adding default comments,
which may be a useful thing to do for the especially tricky
ini options (this PR doesn't add any but adds the ability to do so).
Sadly, this increases the RG99 binary size by 24 KiB.
I'm guessing this is because the map implementation generates
quite a bit of code.
Note that while it might seem that using `std::string` for every key and
value would do a lot of allocations, most of these strings are
small and thus benefit from Small String Optimization (= no allocations).
Anders Jenbo
Gleb Mazovetskiy
Oleksandr Kalko
Trihedraf
Andrettin
staphen