Added CMake support for SDL3.
Now supports including SDL2 or SDL3 as a subdirectory within the project. The system will first check for SDL3, then SDL2. If neither is found, it will attempt find_package(SDL3), followed by find_package(SDL2). If all these checks fail, the process will terminate with an error.

Remove .bc file removal from clean shell for windows configuration.

Clean up library build for the web

- make sure that src/external/rl_gputex.h uses it's own macros
    for printing warnings and allocating memory
- add few additional macros in order to decouple rl_gputex from headers
    that are being included by Raylib (e.g. *_MEMSET, *_NULL and so on)
- make sure that rl_gputex uses RL_*ALLOC, TRACELOG and RLAPI macros
    when (and only when) being included by src/rtextures.c
- replace LOG() and RL_GPUTEX_SHOW_LOG_INFO macros with: RL_GPUTEX_WARN
    and RL_GPUTEX_SHOW_WARN_INFO (this is a breaking change, but it was
    broken and unusable anyway, see:
    https://github.com/raysan5/raylib/issues/5039#issuecomment-3065732596 )
- fixes issue all issues mentioned in:
    https://github.com/raysan5/raylib/issues/5039#issuecomment-3065732596
- remove logging upon successfully saving a file; Raylib does this
    anyway and we want rl_gputex to only print WARNings upon failures;
    see: https://discord.com/channels/426912293134270465/541710686468702250/1394406734306480352
- add additional condition when saving a file; now checks for both
    fwrite() and fclose() failures; before it would warn about both,
    but only return result based on fclose()
- add some notes about the current state of compiling rl_gputex
    without depending on Raylib (spoiler: it's still broken...)
- bump rl_gputex version to 1.1 since this is a potential breaking
    change (only for people attempting to use it without Raylib)

Fixes: https://github.com/raysan5/raylib/issues/5039
Reference: https://discord.com/channels/426912293134270465/541710686468702250/1394403611852931255

I did this with the intention of fixing
https://github.com/raysan5/raylib/issues/5027
but it's hard to tell if it will help in that case or not.
Anyway, bumping the header with mappings should be done once in a while.

I haven't found any Raylib script for doing this, so here's how I did it
step-by-step with CMake rule provided by GLFW (I'm on Linux, but this
should be similar on any other POSIX system):
```sh
$ git clone https://github.com/raysan5/raylib.git
$ cd raylib/src/external/glfw/
$ cmake -B ./build -DGLFW_BUILD_EXAMPLES=OFF -DGLFW_BUILD_TESTS=OFF -DGLFW_BUILD_DOCS=OFF -G "Unix Makefiles"
$ make -C ./build update_mappings
$ rm -fr ./build
```
then I checked, if any mappings were deleted (without updating) with
following shell one-liner:
```sh
  # you must be at 'raylib/src/external/glfw/' when executing this
$ for i in $(git diff ./src/mappings.h | sed -n -e 's/^-"\([0-9a-z]*\),.*$/\1/p'); do grep <./src/mappings.h "$i" > /dev/null || echo "$i"; done;
```
which gave me the following IDs:
```txt
0300000066f700000500000000000000
030000000d0f00001600000000007803
03000000efbe0000edfe000000000000
03000000786901006e70000000000000
050000005e040000e002000030110000
03000000790000000600000010010000
030000000d0f00000d00000000010000
030000000d0f0000d800000072056800
03000000c0160000dc27000001010000
030000008916000000fd000024010000
```
I have checked all those IDs with `git log -p` against
https://github.com/mdqinc/SDL_GameControllerDB
and it seems that all of them were deleted by upstream (I was afraid that
maybe some mappings were added manually by a Raylib contributor and then
overwritten by my patch, but they weren't; All good!)

Allow for the use of raudio stand alone