Fix support for prerelease exits using the new .changeset/pre layout (#711)

* Fix prerelease exit mode selection

* Improve prerelease exit changeset wording

.changeset/pre/eighty-parks-tickle.md

@@ -0,0 +1,17 @@
+---
+"@changesets/action": major
+---
+
+Rename the root action inputs and outputs to better match the sub-actions' conventions.
+
+Inputs:
+
+- `version` -> `version-script`
+- `publish` -> `publish-script`
+- `commit` -> `commit-message`
+- `title` -> `pr-title`
+- `branch` -> `pr-base-branch`
+
+Outputs:
+
+- `pull-request-number` -> `pr-number`