Add support for XLA_DISABLE_FUNCTIONALIZATION flag (#4792)
* Add support for XLA_DISABLE_FUNCTIONALIZATION flag
This change adds support for XLA_DISABLE_FUNCTIONALIZATION. This involves restoring some of the deleted ops when we enabled functionalization and updating some ops to fall back to pre-functionalization state. This change also adds a new test suite that runs test_operations.py with functionalization disabled. Also, see note: [Disabling functionalization].
* Restore view op
* Restore expand op
* Add CPU fallback for convolution_backward
* Update select_symtint and slice.Tensor ops to support XLA_DISABLE_FUNCTIONALIZATION case
* Remove duplicate select.int declaration in xla_native_functions.yaml
* Update new_empty_strided_symint to fallback properly when functionalization is disabled
* Remove debugging print lines
* Run linter
* Add test_operation test suite with functionalization disabled
* Add comments
* Skip tests that will fail when functionalization is disabled
