FindSDL: Add missing variables, SDL::SDL and update doc
This PR updates FindSDL:
- It now sets
SDL_INCLUDE_DIRS
andSDL_LIBRARIES
- I extended it to create the imported target
SDL::SDL
- I altered the documentation to follow the style used by
FindPNG
- It additionally sets
SDL_VERSION
,SDL_VERSION_MAJOR
,SDL_VERSION_MINOR
andSDL_VERSION_PATCH
Fixes: #12911 (closed)
Topic-rename: FindSDL-update
Edited by Frédéric Simonis