Add NuGet packaging step to CI/CD workflow (#405)

* Add NuGet packaging step to CI/CD workflow

For now this just uploads to build artifacts; we will upload to
nuget.org once we've tested that the packages are built correctly.

* Add step to publish NuGet packages

Requires the GitHub org secret named SILLSDEV_PUBLISH_NUGET_ORG to be
present in the org and reachable from this repo.

* Remove Appveyor CI

We don't want two build processes pushing to nuget.org.

* Push .snupkg files as well as .nupkg

* Continue workflow if pushing NuGet packages fails

---------

Co-authored-by: Christopher Hirt <chris@hirtfamily.net>

Author: rmunn

.github/workflows/ci-cd.yml

@@ -96,6 +96,28 @@ jobs:
         shell: cmd
         run: msbuild build\FLExBridge.proj /t:Test /p:Configuration=Release
 
+      - name: Create NuGet packages
+        shell: cmd
+        run: msbuild build\FLExBridge.proj /t:Pack /p:Configuration=Release
+
+      - name: Upload NuGet packages to build artifacts
+        uses: actions/upload-artifact@v4
+        with:
+          name: nuget-packages
+          path: output/*nupkg
+          if-no-files-found: warn
+
+      # --skip-duplicate allows retrying a workflow that failed with a partial push, skipping already published packages and publishing the rest.
+      - name: Publish NuGet packages to nuget.org
+        run: |
+          foreach ($pkg in (Get-ChildItem -Path output -Name -Filter *nupkg)) {
+              dotnet nuget push output/$pkg --skip-duplicate --api-key $env:NUGET_API_KEY --source https://api.nuget.org/v3/index.json
+          }
+        env:
+          NUGET_API_KEY: ${{ secrets.SILLSDEV_PUBLISH_NUGET_ORG }}
+        if: github.event_name != 'pull_request'
+        continue-on-error: true
+
       # All the following are used only when building an installer after a merge
       - name: Build Msi
         id: build_msi