Added SDL_DelayPrecise()

SDL_DelayNS() now passes through to the high precision OS delay function, and SDL_DelayPrecise() tries to busy wait to get as close as possible to the desired wait time.

Fixes https://github.com/libsdl-org/SDL/issues/11141

src/dynapi/SDL_dynapi.sym

@@ -1177,6 +1177,7 @@ SDL3_0.0.0 {
     SDL_wcsstr;
     SDL_wcstol;
     SDL_StepBackUTF8;
+    SDL_DelayPrecise;
     # extra symbols go here (don't modify this line)
   local: *;
 };

src/dynapi/SDL_dynapi_overrides.h

@@ -1202,3 +1202,4 @@
 #define SDL_wcsstr SDL_wcsstr_REAL
 #define SDL_wcstol SDL_wcstol_REAL
 #define SDL_StepBackUTF8 SDL_StepBackUTF8_REAL
+#define SDL_DelayPrecise SDL_DelayPrecise_REAL

src/dynapi/SDL_dynapi_procs.h

@@ -1208,3 +1208,4 @@ SDL_DYNAPI_PROC(wchar_t*,SDL_wcsnstr,(const wchar_t *a, const wchar_t *b, size_t
 SDL_DYNAPI_PROC(wchar_t*,SDL_wcsstr,(const wchar_t *a, const wchar_t *b),(a,b),return)
 SDL_DYNAPI_PROC(long,SDL_wcstol,(const wchar_t *a, wchar_t **b, int c),(a,b,c),return)
 SDL_DYNAPI_PROC(Uint32,SDL_StepBackUTF8,(const char *a, const char **b),(a,b),return)
+SDL_DYNAPI_PROC(void,SDL_DelayPrecise,(Uint64 a),(a),)

src/main/generic/SDL_sysmain_callbacks.c

@@ -65,7 +65,7 @@ int SDL_EnterAppMainCallbacks(int argc, char* argv[], SDL_AppInit_func appinit,
             } else {
                 const Uint64 now = SDL_GetTicksNS();
                 if (next_iteration > now) { // Running faster than the limit, sleep a little.
-                    SDL_DelayNS(next_iteration - now);
+                    SDL_DelayPrecise(next_iteration - now);
                 } else {
                     next_iteration = now; // running behind (or just lost the window)...reset the timer.
                 }

src/render/SDL_render.c

@@ -4948,7 +4948,7 @@ static void SDL_SimulateRenderVSync(SDL_Renderer *renderer)
     elapsed = (now - renderer->last_present);
     if (elapsed < interval) {
         Uint64 duration = (interval - elapsed);
-        SDL_DelayNS(duration);
+        SDL_DelayPrecise(duration);
         now = SDL_GetTicksNS();
     }
 

src/timer/SDL_timer.c

@@ -657,6 +657,11 @@ void SDL_Delay(Uint32 ms)
 }
 
 void SDL_DelayNS(Uint64 ns)
+{
+    SDL_SYS_DelayNS(ns);
+}
+
+void SDL_DelayPrecise(Uint64 ns)
 {
     Uint64 current_value = SDL_GetTicksNS();
     Uint64 target_value = current_value + ns;