ci: Split mainline pipeline and add support for GitHub releases (#2900)

* ci: Add mock build alternative for fast testing

* ci: Always cache build

* ci: Extract steps to download build stage artifacts

* ci: Add template to release to GitHub

* ci: Add template to release to Azure Universal Artifacts

* ci: Split mainline to two pipelines

.ci/templates/release-github.yml

@@ -0,0 +1,11 @@
+steps:
+  - template: ./release-download.yml
+  - task: GitHubRelease@0
+    inputs:
+      action: 'create'
+      title: 'yuzu $(BuildName) #$(Build.BuildId)'
+      assets: '$(Build.ArtifactStagingDirectory)/*'
+      gitHubConnection: $(GitHubReleaseConnectionName)
+      repositoryName: '$(Build.Repository.Name)'
+      target: '$(Build.SourceVersion)'
+      tagSource: 'auto'