This ensures the python label is used for all python code blocks for
consistency.
## Test Plan
Visual inspection of all changes via git client ensuring no other
changes were made in error.
Split out of #8044: In preview style, ellipsis are also collapsed in
non-stub files. This should only affect function/class contexts since
for other statements stub are generally not used. I've updated our tests
to use `pass` instead to reflect this, which makes tracking the preview
style changes much easier.
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## Summary
This PR adds tests that verify that the magic trailing comma is not respected if disabled in the formatter options.
Our test setup now allows to create a `<fixture-name>.options.json` file that contains an array of configurations that should be tested.
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## Test Plan
It's all about tests :)
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