[SYCL][NewOffloadModel] Update SYCL device library generation for new offloading model

[YixingZhang007]

This pull request refactors the SYCL device library build and end-to-end tests to support the new offloading model, while maintaining backward compatibility for the old offloading model, with the following key changes.

1. The default device library (such as libsycl-itt-compiler-wrappers.o) is now compiled using the new offloading model, and the library ending with .new.o (such as libsycl-itt-compiler-wrappers.new.o) has been renamed to .old.o (such as libsycl-itt-compiler-wrappers.old.o), representing builds with the old offloading model. These changes are made in libdevice/cmake/modules/SYCLLibdevice.cmake.
2. The end-to-end tests in sycl/test-e2e/Config/kernel_from_file.cpp and sycl/test-e2e/SeparateCompile/test.cpp have been updated. The tests now validate both the new offloading model, and the backward compatibility for the old model (using clang-offload-bundler to extract device code from libraries).

[YixingZhang007]

The modifications to set the new offloading model as default in this PR were directly copied from (#15121). These changes will be removed once CI confirms there are no regressions.