Use stages pipeline

- #11924
- change default-build.yml to use job.yml
  - remove unused parameters e.g. `matrix`, `poolName`, `variables`
  - use `enableMicrobuild` and `enablePublishTestResults` to eliminate duplicate build steps
- change ci.yml to use stages and post-build.yml
  - add use of publish-build-assets.yml and post-build.yml

Author: dougbu