Include symlinks and root_symlinks in Python ZIPs

[fmeum]

Work towards #17941

[fmeum]

@rickeylev I couldn't find where and how to test this, could you give me some pointers?

[rickeylev]

Sorry, didn't see this till now.

Hm, I'm not sure. You want to verify the contents of a param file created when an action is run.

Try getting a handle on the PythonZipper action and looking at its inputs. Maybe the param file is in there. BuildViewTestCase.getGeneratingAction and ActionsTestUtil might help here.

Here's an example of how the regular template-expansion codepath has its action inspected: https://cs.opensource.google/bazel/bazel/+/master:src/test/java/com/google/devtools/build/lib/bazel/rules/python/BazelPyBinaryConfiguredTargetTest.java;l=76?q=f:test%20f:python%20getgeneratingaction&ss=bazel%2Fbazel:src%2F

Otherwise, I think there's a flag that makes params files persist after building; try that and then root around in bazel-out for the param file?

[rickeylev]

LGTM, just needs tests.