Merge branch 'release/3.1' into master

.azure/pipelines/ci.yml

.azure/pipelines/jobs/codesign-xplat.yml

.azure/pipelines/jobs/default-build.yml

Directory.Build.props

Directory.Build.targets

build.ps1

build.sh

docs/PreparingPatchUpdates.md

docs/ProjectProperties.md

docs/ReferenceResolution.md

eng/Baseline.Designer.props

eng/Baseline.xml

eng/Build.props

eng/CodeGen.proj

eng/Dependencies.props

eng/GenAPI.exclusions.txt

eng/PatchConfig.props

eng/PlatformManifest.txt

eng/PoliCheckExclusions.xml

eng/ProjectReferences.props