[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.

[sarnex]

thanks for the PR! one higher level comment below

[sarnex]

my worry here is that it seems this PR enables the new offload model by default for some but not all compilation modes, and since we are setting the default device library files to be the new offloading model (since we pass --offload-new-driver), i am not sure of those compilation modes using the old offload model will be able to use libdevice. the new offload model supports using old libdevice files, but i had to explicitly implement that to get it working and i don't think anyone did the opposite case since it wasn't expected to be be needed, but it's possible it works automagically. can you make sure the cases using the old offload model still work?