Use floating point values for viewport, clip rectangle, and texture sizes

These are integer values internally, but the API has been changed to make it easier to mix other render code with querying those values.

Fixes https://github.com/libsdl-org/SDL/issues/7519

test/testgeometry.c

@@ -121,11 +121,11 @@ static void loop(void)
         SDL_RenderClear(renderer);
 
         {
-            SDL_Rect viewport;
+            SDL_FRect viewport;
             SDL_Vertex verts[3];
             float a;
             float d;
-            int cx, cy;
+            float cx, cy;
 
             /* Query the sizes */
             SDL_GetRenderViewport(renderer, &viewport);