Sign UWP artifacts (dotnet/core-setup#2770)
* The SignUwpFiles target wasn't attached anywhere. Move the files it wants to sign into the SignBinaries target.
* Updated baseline.props
* appx file is not produced during the build binaries step and is not
getting baselined
* Add signing of appx to "Sign Msi and cab" step
* Remove appx file signing
* Ignore casing for baseline comparison
* Fix casing
* Fix parens
Commit migrated from https://github.com/dotnet/core-setup/commit/
73e57cebd9c71728d409407b6c4b7f7f9a56fa02