[SYCL][NFC] Clean-up platform.hpp includes (#10569)

Author: bader

sycl/include/sycl/detail/backend_traits.hpp

@@ -9,7 +9,6 @@
 #pragma once
 
 #include <sycl/backend_types.hpp>
-#include <sycl/detail/common.hpp>
 
 namespace sycl {
 inline namespace _V1 {

sycl/include/sycl/device_selector.hpp

@@ -8,7 +8,7 @@
 
 #pragma once
 
-#include <sycl/detail/defines.hpp>
+#include <sycl/detail/defines_elementary.hpp>
 #include <sycl/detail/export.hpp>
 
 #include <functional>

sycl/include/sycl/platform.hpp

@@ -9,14 +9,11 @@
 #pragma once
 
 #include <sycl/aspects.hpp>
-#include <sycl/context.hpp>
 #include <sycl/detail/backend_traits.hpp>
-#include <sycl/detail/common.hpp>
 #include <sycl/detail/export.hpp>
 #include <sycl/detail/info_desc_helpers.hpp>
 #include <sycl/detail/owner_less_base.hpp>
 #include <sycl/device_selector.hpp>
-#include <sycl/ext/oneapi/weak_object_base.hpp>
 
 #include <utility>
 
@@ -25,8 +22,9 @@ inline namespace _V1 {
 // TODO: make code thread-safe
 
 // Forward declaration
-class device_selector;
 class device;
+class context;
+
 template <backend BackendName, class SyclObjectT>
 auto get_native(const SyclObjectT &Obj)
     -> backend_return_t<BackendName, SyclObjectT>;