Updated structure and field names for consistency

Type names are camel case and field names are snake case except for fields ending in id, which are capitalized.

Fixes https://github.com/libsdl-org/SDL/issues/6955

test/testver.c

@@ -19,8 +19,8 @@
 
 int main(int argc, char *argv[])
 {
-    SDL_version compiled;
-    SDL_version linked;
+    SDL_Version compiled;
+    SDL_Version linked;
 
     /* Enable standard application logging */
     SDL_LogSetPriority(SDL_LOG_CATEGORY_APPLICATION, SDL_LOG_PRIORITY_INFO);