Build distribution when running quick-check workflow

The action requires the generated distribution to committed to the 'dist' directory.
During regular development this step causes a number of problems:
- It's easy to forget to add/commit these generated files.
- It's very difficult/impossible to merge/rebase commits that involve generated files
- These file add unnecessary bulk to the git history

With this change, the quick-check workflow will first build the distribution and then
use the generated output for testing. Building and committing these files will only be
required when merging into the 'main' branch.

.github/actions/download-dist/action.yml

@@ -0,0 +1,12 @@
+name: 'Download dist'
+# Downloads a 'dist' directory artifact that was uploaded in an earlier step
+# We control this with an environment variable to allow for easier global configuration.
+runs:
+  using: "composite"
+  steps: 
+    - name: Download dist
+      if: ${{ env.DOWNLOAD_DIST == 'true' }}
+      uses: actions/download-artifact@v2
+      with:
+        name: dist
+        path: dist/