wikiheaders: bridge wiki Category docs to the headers!

Did an initial cleanup on the headers and wrote a few pieces of documentation,
but this needs more work to fill out the documentation.

include/SDL3/SDL_test_fuzzer.h

@@ -20,8 +20,6 @@
 */
 
 /**
- *  \file SDL_test_fuzzer.h
- *
  *  Fuzzer functions of SDL test framework.
  *
  *  This code is a part of the SDL test library, not the main SDL library.
@@ -49,7 +47,6 @@ extern "C" {
 
 
 /**
- * \file
  * Note: The fuzzer implementation uses a static instance of random context
  * internally which makes it thread-UNsafe.
  */