Add getter and setter methods for compile_backend across accelerators. (#5299)
Add getter and setter methods for `compile_backend` across accelerators,
which provide a mechanism to retrieve the compile backend. These APIs
handle user-defined backend selection and raise a `ValueError` with
informative error messages for unsupported backends.
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Co-authored-by: Olatunji Ruwase <olruwase@microsoft.com>
Co-authored-by: Logan Adams <114770087+loadams@users.noreply.github.com>