[Python] export cython module for external project

[ashione]

Why are these changes needed?

A lot of cython data types have been defined in ray cython module, but outside project cannot reuse these since ray doesn't export all of *.pxd files.

To fix mobius python building error (https://github.com/ray-project/mobius/runs/5740167581?check_suite_focus=true) : no found ray common.pxd, etc. ,

According to cython document https://cython.readthedocs.io/en/latest/src/userguide/source_files_and_compilation.html
we might add this package_data parameter in setup.py

setup(
    package_data = {
        'my_package': ['*.pxd'],
        'my_package/sub_package': ['*.pxd'],
    },
    ...
)

Related issue number

Checks

• I've run scripts/format.sh to lint the changes in this PR.
• I've included any doc changes needed for https://docs.ray.io/en/master/.
• I've made sure the tests are passing. Note that there might be a few flaky tests, see the recent failures at https://flakey-tests.ray.io/
• Testing Strategy
  • Unit tests
  • Release tests
  • This PR is not tested :(

[ashione]

I upload a temp dist package for mobius building in this branch source code.
https://ray-mobius-us.oss-us-west-1.aliyuncs.com/ci/macos/ray-2.0.0.dev0-cp38-cp38-macosx_11_0_x86_64.whl

[jovany-wang]

Looks good to me. Maybe it needs to be approved by @ericl for code owner purpose.

[jovany-wang]

@ashione Could you check the CI result?

[ashione]

@ashione Could you check the CI result?

These failures are unrelated with changes.

[jovany-wang]

Lint failure is unrelated.