Enhance pr_changed_files with exit codes and string output

[iangmaia]

Follow up to the discussion started on woocommerce/woocommerce-ios#15086 (comment).

This PR adds both exit codes (default mode) and "true" "false" output (using --stdout flag) to the pr_changed_files command, updating documentation and tests accordingly.

---

• I have considered if this change warrants release notes and have added them to the appropriate section in the CHANGELOG.md if necessary.

[AliSoftware]

👌

[AliSoftware]

Apart from the test missing to assert expected empty output (which I think is worth fixing before merging), the rest looks good, so I'm approving to unblock, supposing you'll fix that test helper.

I've also left a nitpick for implementation of exit_result, but up to you if you want to adopt it, and not a blocker.

PS: 🎗️ Reminder to update your P2 post accordingly once this ships, to provide up-to-date call examples.

[AliSoftware]

💭 Future improvement idea I just had while re-reading the whole code: I wonder if the implementation wouldn't read better (especially the call site of this internal function) if we had 2 separate methods instead:

exit_true() {
    if [[ "$use_stdout" == "true" ]]; then
        echo "true"
    fi
    exit 0
}

exit_false() {
    if [[ "$use_stdout" == "true" ]]; then
        echo "false"
        exit 0
    fi
    exit 1
}

Then the call sites would read exit_false() instead of exit_result 1, which arguably makes it easier to understand when reading the implementation… 🤔 🤷

That's just a nitpick though, and definitively not a blocker.

[iangmaia]

Great idea though, makes it indeed more readable than exit_result 1! Implemented on ecd08ee