[SYCL] Add SYCL 2020 image classes (#9308)

This commit adds the SYCL 2020 image classes sampled_image and
unsampled_image, together with their constituents. The implementation
leverages the implementation of the existing SYCL 1.2.1 image class.

Since the corresponding accessor classes are still to be added, this
commit does not include the `get_access` member functions.

---------

Signed-off-by: Larsen, Steffen <[email protected]>

Author: steffenlarsen

sycl/include/sycl/access/access.hpp

@@ -62,6 +62,8 @@ enum class decorated : int { no = 0, yes = 1, legacy = 2 };
 using access::target;
 using access_mode = access::mode;
 
+enum class image_target : unsigned int { device = 0, host_task = 1 };
+
 template <access_mode mode> struct mode_tag_t {
   explicit mode_tag_t() = default;
 };

sycl/include/sycl/ext/oneapi/owner_less.hpp

@@ -15,6 +15,7 @@
 #include <sycl/device.hpp>
 #include <sycl/event.hpp>
 #include <sycl/ext/oneapi/weak_object.hpp>
+#include <sycl/image.hpp>
 #include <sycl/kernel.hpp>
 #include <sycl/kernel_bundle.hpp>
 #include <sycl/platform.hpp>
@@ -76,6 +77,15 @@ template <typename DataT, int Dimensions, typename AllocatorT>
 struct owner_less<buffer<DataT, Dimensions, AllocatorT>>
     : public detail::owner_less_base<buffer<DataT, Dimensions, AllocatorT>> {};
 
+template <int Dimensions, typename AllocatorT>
+struct owner_less<unsampled_image<Dimensions, AllocatorT>>
+    : public detail::owner_less_base<unsampled_image<Dimensions, AllocatorT>> {
+};
+
+template <int Dimensions, typename AllocatorT>
+struct owner_less<sampled_image<Dimensions, AllocatorT>>
+    : public detail::owner_less_base<sampled_image<Dimensions, AllocatorT>> {};
+
 template <typename DataT, int Dimensions, access_mode AccessMode,
           target AccessTarget, access::placeholder isPlaceholder>
 struct owner_less<