[llvm] [libsycl] Implement memcpy API (PR #205369)

[Yury Plyakhin via llvm-commits]

================
@@ -331,6 +331,36 @@ class _LIBSYCL_EXPORT queue {
                                        std::forward<Rest>(rest)...);
   }
 
+  /// Submits a memory copy operation from one USM or host pointer to another.
+  ///
+  /// \param dest is the pointer to copy to.
+  /// \param src is the pointer to copy from.
+  /// \param numBytes is the number of bytes to copy.
+  /// \return an event that represents the status of the operation.
+  event memcpy(void *dest, const void *src, std::size_t numBytes);
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YuriPlyakhin wrote:

it seems it is how it specified in the standard:
```
  event memcpy(void* dest, const void* src, std::size_t numBytes);
  event memcpy(void* dest, const void* src, std::size_t numBytes, event depEvent);
  event memcpy(void* dest, const void* src, std::size_t numBytes,
               const std::vector<event>& depEvents);
```

https://github.com/llvm/llvm-project/pull/205369