Rename root action inputs and outputs

[bluwy]

Follow-up on #668. I also copied the input descriptions from the sub-actions as they're more up-to-date and concise. And also copied the order of them.

Inputs:

• version -> version-script
• publish -> publish-script
• commit -> commit-message
• title -> pr-title
• branch -> pr-base-branch

Outputs:

• pull-request-number -> pr-number

---

These changes are kinda huge the more I see it. Should we consider making them work but log a warning instead?

[Andarist]

This and previous PR missed renaming the lists under https://github.com/changesets/action/#inputs and https://github.com/changesets/action/#outputs