[sdl2pp] Portfile installs cmake files into wrong directory

### Is your feature request related to a problem? Please describe.

The existing port for sdl2pp has this:

```
vcpkg_cmake_config_fixup(CONFIG_PATH "lib/cmake")
```

But it should be

```
# Upstream installs config to lib/cmake/SDL2pp/ — fix-up must target that
# exact directory so files land at share/sdl2pp/ (not share/sdl2pp/SDL2pp/).
vcpkg_cmake_config_fixup(CONFIG_PATH "lib/cmake/SDL2pp")
```

As currently written, the port prevents use of the `SDL2pp::SDL2pp` cmake target because cmake cant find the cmake target files for SDL2pp (they are in the wrong directory).

### Proposed solution

See above for proposed fix.

### Describe alternatives you've considered

_No response_

### Additional context

_No response_

Locate the sdl2pp portfile and inspect its vcpkg_cmake_config_fixup entry. Verify the upstream SDL2pp config directory and confirm that the SDL2pp::SDL2pp target files are installed under share/sdl2pp/ so CMake can find them.

Written by the indexing model from the issue text.