[xla:ffi] Add Python-based tests for type-safe custom calls on CPU platform
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[xla:ffi] Add Python-based tests for type-safe custom calls on CPU platform

Implements #10062. This change only adds test cases, all other changes required for Python support are already merged.

FUTURE_COPYBARA_INTEGRATE_REVIEW=https://github.com/tensorflow/tensorflow/pull/44950 from Intel-tensorflow:yimei/fuse_old_bn e09d450b1fec79c547e6599040aad5ccbb8b96fc
