Everything in SDL3 up to the ABI lock is reported as available since 3.1.3.
Everything else will be reported as since 3.2.0 (what will be the first
official release).
Also ran a Perl script over the headers to change everything to 3.1.3 that
wasn't an API function, since fnsince.pl can't manage those. If there's a
macro or datatype that has snuck in that needs to be 3.2.0 instead, we'll
have to manually fix it up, but it shouldn't be a big deal in any case.
Reference PR #11304.
The specific cases here were SDL_size_mul_overflow_builtin and
SDL_size_add_overflow_builtin, which are forced-inline symbols in
SDL_stdinc.h that have to exist, but aren't really part of the public API,
and thus shouldn't be exported as documentation.
I ran this script in the include directory:
```sh
sed -i '' -e 's,#include "\(SDL.*\)",#include <SDL3/\1>,' *.h
```
I ran this script in the src directory:
```sh
for i in ../include/SDL3/SDL*.h
do hdr=$(basename $i)
if [ x"$(echo $hdr | egrep 'SDL_main|SDL_name|SDL_test|SDL_syswm|SDL_opengl|SDL_egl|SDL_vulkan')" != x ]; then
find . -type f -exec sed -i '' -e 's,#include "\('$hdr'\)",#include <SDL3/\1>,' {} \;
else
find . -type f -exec sed -i '' -e '/#include "'$hdr'"/d' {} \;
fi
done
```
Fixes https://github.com/libsdl-org/SDL/issues/6575
