api: Added SDL_CreateTemporaryProperties() for more-efficient throwaway props.

[icculus]

This is an attempt at a limited-but-lower-overhead Properties object that could be useful for throwaway SDL_PropertiesID...namely, the type we use for SDL_Create*WithProperties functions.

And example of updating testyuv.c to use it:

diff --git a/test/testyuv.c b/test/testyuv.c
index 81ed2b734..93b11f6ef 100644
--- a/test/testyuv.c
+++ b/test/testyuv.c
@@ -619,12 +619,16 @@ int main(int argc, char **argv)
 
     output[0] = SDL_CreateTextureFromSurface(renderer, original);
     output[1] = SDL_CreateTextureFromSurface(renderer, converted);
-    props = SDL_CreateProperties();
-    SDL_SetNumberProperty(props, SDL_PROP_TEXTURE_CREATE_COLORSPACE_NUMBER, yuv_colorspace);
-    SDL_SetNumberProperty(props, SDL_PROP_TEXTURE_CREATE_FORMAT_NUMBER, yuv_format);
-    SDL_SetNumberProperty(props, SDL_PROP_TEXTURE_CREATE_ACCESS_NUMBER, SDL_TEXTUREACCESS_STREAMING);
-    SDL_SetNumberProperty(props, SDL_PROP_TEXTURE_CREATE_WIDTH_NUMBER, original->w);
-    SDL_SetNumberProperty(props, SDL_PROP_TEXTURE_CREATE_HEIGHT_NUMBER, original->h);
+    {
+        const SDL_TemporaryPropertyItem texture_prop_items[] = {
+            { SDL_PROP_TEXTURE_CREATE_COLORSPACE_NUMBER, SDL_PROPERTY_TYPE_NUMBER, { .n = yuv_colorspace } },
+            { SDL_PROP_TEXTURE_CREATE_FORMAT_NUMBER, SDL_PROPERTY_TYPE_NUMBER, { .n = yuv_format } },
+            { SDL_PROP_TEXTURE_CREATE_ACCESS_NUMBER, SDL_PROPERTY_TYPE_NUMBER, { .n = SDL_TEXTUREACCESS_STREAMING } },
+            { SDL_PROP_TEXTURE_CREATE_WIDTH_NUMBER, SDL_PROPERTY_TYPE_NUMBER, { .n = original->w } },
+            { SDL_PROP_TEXTURE_CREATE_HEIGHT_NUMBER, SDL_PROPERTY_TYPE_NUMBER, { .n = original->h } }
+        };
+        props = SDL_CreateTemporaryProperties(texture_prop_items, SDL_arraysize(texture_prop_items));
+    }
     output[2] = SDL_CreateTextureWithProperties(renderer, props);
     SDL_DestroyProperties(props);
     if (!output[0] || !output[1] || !output[2]) {

If following the rules for these objects (read-only, thread unsafe, etc), they could be used in other situations, as they can be used anywhere an SDL_PropertiesID is expected.

Fixes #14436.

[slouken]

Let's hold this for 3.6