[SYCL] Optimize event_impl::setContextImpl

[PatKamin]

Copy a shared_ptr directly instead of using more expensive make_shared_from_this.

[lslusarczyk]

the best API for shared pointer (generally for moveable classes) is to take it by value, not "const &"
"const &" guarantees there will be at least one copy needed when storing this object, while taking by value and calling move allows called to pass rvalue and avoid copy at all

so, in ideal worlds we will take by value and call MContext = std::move(Context);

however getContextImplPtr returns "const &" so copy can not be avoided

Please explain why shared_from_this cost is bigger than copying.

[PatKamin]

Closing as gains can be neglected