[SYCL][Bindless] Add default constructor to bindless sampler

sycl/doc/extensions/experimental/sycl_ext_oneapi_bindless_images.asciidoc

@@ -652,18 +652,24 @@ struct bindless_image_sampler {
                          float minMipmapLevelClamp, float maxMipmapLevelClamp,
                          float maxAnisotropy);
 
-  sycl::addressing_mode addressing;
-  sycl::coordinate_normalization_mode coordinate;
-  sycl::filtering_mode filtering;
-  sycl::filtering_mode mipmap_filtering;
-  float min_mipmap_level_clamp;
-  float max_mipmap_level_clamp;
-  float max_anisotropy;
+  sycl::addressing_mode addressing = sycl::addressing_mode::none;
+  sycl::coordinate_normalization_mode coordinate =
+      sycl::coordinate_normalization_mode::unnormalized;
+  sycl::filtering_mode filtering = sycl::filtering_mode::nearest;
+  sycl::filtering_mode mipmap_filtering = sycl::filtering_mode::nearest;
+  float min_mipmap_level_clamp = 0.f;
+  float max_mipmap_level_clamp = 0.f;
+  float max_anisotropy = 0.f;
 };
 
 }
 ```
 
+The `bindless_image_sampler` shall be default constructible and follow by-value 
+semantics. The value for the addressing mode, `addressing_mode::none`, 
+represents the backend's default addressing mode. On CUDA this is `Wrap`, i.e. 
+`addressing_mode::repeat`.
+
 `mipmap_filtering` dictates the method in which sampling between mipmap 
 levels is performed.
 
@@ -1997,4 +2003,6 @@ These features still need to be handled:
                    restrictions on image types
 |4.8|2023-10-25| - Change the name of `map_external_memory_array` to 
                    `map_external_image_memory` to avoid CUDA terminology
+|4.9|2023-11-13| - Add that the bindless sampler is default constructible 
+                   and follows by-value semantics
 |======================

sycl/include/sycl/ext/oneapi/bindless_images_sampler.hpp

@@ -33,10 +33,13 @@ struct bindless_image_sampler {
         max_mipmap_level_clamp(maxMipmapLevelClamp),
         max_anisotropy(maxAnisotropy) {}
 
-  sycl::addressing_mode addressing;
-  sycl::coordinate_normalization_mode coordinate;
-  sycl::filtering_mode filtering;
-  sycl::filtering_mode mipmap_filtering;
+  bindless_image_sampler() = default;
+
+  sycl::addressing_mode addressing = sycl::addressing_mode::none;
+  sycl::coordinate_normalization_mode coordinate =
+      sycl::coordinate_normalization_mode::unnormalized;
+  sycl::filtering_mode filtering = sycl::filtering_mode::nearest;
+  sycl::filtering_mode mipmap_filtering = sycl::filtering_mode::nearest;
   float min_mipmap_level_clamp = 0.f;
   float max_mipmap_level_clamp = 0.f;
   float max_anisotropy = 0.f;

sycl/test-e2e/bindless_images/sampling_2D.cpp

@@ -35,11 +35,18 @@ int main() {
   }
 
   try {
-    sycl::ext::oneapi::experimental::bindless_image_sampler samp(
+    sycl::ext::oneapi::experimental::bindless_image_sampler tempSamp(
         sycl::addressing_mode::repeat,
         sycl::coordinate_normalization_mode::normalized,
         sycl::filtering_mode::linear);
 
+    // Default constructible sampler
+    sycl::ext::oneapi::experimental::bindless_image_sampler samp;
+
+    // Sampler follows by-value semantics
+    sycl::ext::oneapi::experimental::bindless_image_sampler tempSamp2(tempSamp);
+    samp = tempSamp2;
+
     // Extension: image descriptor -- can use the same for both images
     sycl::ext::oneapi::experimental::image_descriptor desc(
         {width, height}, sycl::image_channel_order::rgba,