[SYCL] address regressions from making backend a property of platform (#9260)

Signed-off-by: Sergey V Maslov <[email protected]>

Author: smaslov-intel

sycl/source/detail/event_impl.hpp

@@ -251,7 +251,10 @@ class event_impl {
 
   bool isContextInitialized() const noexcept { return MIsContextInitialized; }
 
-  ContextImplPtr getContextImplPtr() const { return MContext; }
+  ContextImplPtr getContextImplPtr() {
+    ensureContextInitialized();
+    return MContext;
+  }
 
 protected:
   // When instrumentation is enabled emits trace event for event wait begin and

sycl/unittests/pi/BackendString.hpp

@@ -7,7 +7,7 @@
 #include <detail/plugin.hpp>
 
 namespace pi {
-inline const char *GetBackendString(const sycl::detail::plugin &Plugin) {
+inline std::string GetBackendString(const sycl::detail::plugin &Plugin) {
   std::stringstream Str;
   for (sycl::backend Backend :
        {sycl::backend::opencl, sycl::backend::ext_oneapi_level_zero,
@@ -17,6 +17,6 @@ inline const char *GetBackendString(const sycl::detail::plugin &Plugin) {
       Str << Backend;
     }
   }
-  return Str.str().c_str();
+  return Str.str();
 }
 } // namespace pi