- #11924
- change ci.yml to use stages and post-build.yml
  - add use of publish-build-assets.yml and post-build.yml
  - create manifests and push to artifacts in last build step of each job
    - pass more MSBuild properties into those builds
    - use Arcade to publish installers
  - use distinct `$(AssetManifestFileName)` values per job
    - set global property to override what's hard-coded in Publish.proj
- change codesign-xplat.yml to use empty.proj and normal Arcade signing and publication process
  - remove XPlatPackageSigner.proj
- change default-build.yml to use job.yml
  - remove unused parameters e.g. `matrix`, `poolName`, `variables`
  - use `enableMicrobuild` and `enablePublishTestResults` to eliminate duplicate build steps
- add .dll's and .exe's as files to sign w/ Microsoft400
  - add signcheck exclusions
- remove custom manifest generation i.e. the `GenerateBuildAssetManifest` target and related artifacts
- update docker infrastructure to use same paths in and out of the container
  - avoids problems adding to artifacts from within the builds
- correct typo in build.sh
- use `$env:DOTNET_INSTALL_DIR` in `DotNetCommands`
  - relax expectations that an arch-specific folder exists under (say) `$env:DOTNET_HOME`
  - avoids need to define `$env:DOTNET_HOME` in all jobs on CI
- update dependencies from dotnet/arcade build '20190908.2'
  - upgrade to eg. Arcade SDK '1.0.0-beta.19458.2' package version
  - pick up dotnet/arcade@dd593acc8b08 fix
    - enable use of `%(PublishFlatContainer)` metadata and correct signing validation issues
- use `$(DotNetFinalVersionKind)` in preparation for servicing builds
  - set `$(IsStableBuild)` for use in Arcade infrastructure
- disable signing validation for now (see #13864)

nits:
- upload logs in first artifact
- remove attempts to package non-existent VSIX
  - follow-up to 29cf7ecb
- respect verbosity setting in build.sh
- add more information to Artifacts.md
- enable test signing in internal PRs