Reuse the same relative position bias in every layers #2258

Job	Run time
build-python-wheels (ubuntu-20.04, auto64)	42m 11s
build-python-wheels (macos-11, auto64)	44m 9s
build-python-wheels (windows-2019, auto64)	58m 39s
build-python-wheels (ubuntu-20.04, aarch64)	1h 48m 20s
build-python-wheels (macos-11, arm64)	14m 7s
build-and-test-cpp-x86_64 (ubuntu-20.04, mkl)	7m 27s
build-and-test-cpp-x86_64 (ubuntu-20.04, dnnl)	6m 14s
build-and-test-cpp-x86_64 (macos-11, mkl)	10m 19s
build-and-test-cpp-x86_64 (macos-11, dnnl)	9m 51s
build-and-push-docker-images	32m 26s
build-and-test-cpp-aarch64 (openblas)	6m 1s
check-python-style	9s
test-python-wheels (ubuntu-20.04)	10m 26s
test-python-wheels (macos-11)	6m 6s
test-python-wheels (windows-2019)	3m 38s
build-and-deploy-docs	39s
publish-python-wheels-on-pypi	0s
	6h 0m 42s

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