Automatically dispatch emscripten release tag action (#1442)

This PR add several features to release automation:

1. The existing tag-release job has an output that indicates whether the
triggering commit
    is a release (i.e. whether it matches the regex)
2. The new followup job runs a new script which fetches the recent
emscripten-releases
revisions, reads the DEPS file from the 'latest' release in
emscripten-releases-tags.json
to find the corresponding emscripten revision and writes it into the
environment
2. The final step reads the emscripten revision from the environment and
creates a
workflow_dispatch event to run the tag-release.yml job on the emscripten
repo

.github/workflows/create-release.yml

@@ -23,5 +23,10 @@ jobs:
         uses: peter-evans/create-pull-request@v6
         with:
           title: Release ${{ env.RELEASE_VERSION }}
-          commit-message: Release ${{ env.RELEASE_VERSION }}
+          commit-message: |
+            Release ${{ env.RELEASE_VERSION }}
+          body: |
+            With emscripten-releases revisions:
+              https://chromium.googlesource.com/emscripten-releases/+/${{ inputs.lto-sha }} (LTO)
+              https://chromium.googlesource.com/emscripten-releases/+/${{ inputs.nonlto-sha }} (asserts)
           delete-branch: true