[llvm] [libsycl] Add USM alloc & release funcs (PR #181120)

[Alexey Bader via llvm-commits]

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@@ -105,4 +105,12 @@ TODO for added SYCL classes
   * ``has_extension``: deprecated API, to implement on RT level with ``device::has``
 
 * device selection: to add compatibility with old SYCL 1.2.1 device selectors, still part of SYCL 2020 specification
+* ``context``: to implement get_info, properties & public constructors once context support is added to liboffload
+* ``queue``: to implement USM methods, to implement synchronization methods, to implement submit & copy with accessors (low priority), get_info & properties, ctors that accepts context (blocked by lack of liboffload support)
+* ``property_list``: to fully implement and integrate to existing SYCL runtime classes supporting it
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bader wrote:

This PR provides the context and justification for incomplete implementation.
It can be useful to lay out the phased upstream approach we are taking in some document.

https://github.com/llvm/llvm-project/pull/181120