[SYCL] Return ref to shared_ptr from handler::getOrInsertHandlerKernelBundle()

[Alexandr-Konovalov]

It's reference to impl of handler, so it's correct to return the reference.

[Alexandr-Konovalov]

arc fails tracked by https://github.com/intel/llvm/issues/18668

[Alexandr-Konovalov]

@uditagarwal97 , what do you think about it?

[Alexandr-Konovalov]

IMO, this should be returning raw pointer with the kernel_bundle_impl updated to be inherited from std::enable_shared_from_this, similar to what I'm doing for other classes (e.g. #18795 with links in the description or current WIP #18767)

Thanks for the idea! [SYCL] enable_shared_from_this for kernel_bundle_impl #18899 opened.