Add Csproj pack infra for packages with ref and runtime assemblies and symbols. ...

Add Csproj pack infra for packages with ref and runtime assemblies and symbols. (#54250)

* add infra for adding ref and runtime assemblies

delete the project

add a comment

move the warning disable to cenral location

moving props/targets to packaging.props and packaging.targets

use intellisense package for ref and runtime xml files

add comments, flag for ref assemblies, remove xml from runtimes, use outputItem to get the reference assembly

addressing some more feedback

remove ref assemblies

add suppression file and update package validatio

* move PackageValidationBaselineVersion to packaging.targets

* update the package validation version