feat: expose cache-primary-key output (#597) (#1088)

* feat: expose cache-primary-key output (#597)

Expose the primary cache key computed by the caching logic as a new
`cache-primary-key` action output, so workflows can compose the built-in
setup-java cache key with actions/cache or actions/cache/restore across
steps and dependent jobs.

- src/cache.ts: set the `cache-primary-key` output in restore()
- action.yml: declare the new output
- README.md: document the new output
- __tests__/cache.test.ts: assert the output is set
- dist: rebuild

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

* Potential fix for pull request finding

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

* Potential fix for pull request finding

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

* Potential fix for pull request finding

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

* chore: rebuild dist

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

---------

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

dist/cleanup/index.js

@@ -99735,6 +99735,7 @@ async function restore(id, cacheDependencyPath) {
     const primaryKey = await computeCacheKey(packageManager, cacheDependencyPath);
     core.debug(`primary key is ${primaryKey}`);
     core.saveState(STATE_CACHE_PRIMARY_KEY, primaryKey);
+    core.setOutput(STATE_CACHE_PRIMARY_KEY, primaryKey);
     // No "restoreKeys" is set, to start with a clear cache after dependency update (see https://github.com/actions/setup-java/issues/269)
     const matchedKey = await cache.restoreCache(packageManager.path, primaryKey);
     if (matchedKey) {