Clean-up pkgproj leftovers in libs and apply fixes

Remove any pkgproj infrastructure that was only used by src/libraries
(which is the majority). Delete the packageindex *YAY*.
Update the documentation that covered the packageindex and the pkgprojs.

Avoid any incremental builds during packaging by removing
libraries-packages.proj and use src.proj for packaging instead. Make use
of the `GeneratePackageOnBuild` property to build package during the
allconfigurations without requiring a different entry target.

Fix the addition of the DocumentationFile during packaging when
`GeneratePackageOnBuid` is used by hooking onto the
`DocumentationProjectOutputGroup` that NuGet uses and replacing the
generated documentation file with the one that comes via the
intellisense package.
Also introduce a property to choose the generated documentation file
over the one from the intellisense package:
<UseIntellisenseDocumentationFile>false</UseIntellisenseDocumentationFile>

Removing a few leftover PackageDescription properties from the projects'
Directory.Build.props file.

Cleaning up properties in Directory.Build.props & Directory.Build.targets
files.

Author: ViktorHofer

Directory.Build.targets

@@ -54,8 +54,6 @@
     <PackageDescription Condition="'$(PackageDescription)' == '' and '$(UseRuntimePackageDisclaimer)' == 'true'">$(RuntimePackageDisclaimer)</PackageDescription>
     <!-- Keep in sync as required by the Packaging SDK in Arcade. -->
     <Description>$(PackageDescription)</Description>
-    <!-- BeforePack hook should be removed after porting all the projects to dotnet pack. -->
-    <BeforePack>$(BeforePack);AddNETStandardCompatErrorFileForPackaging</BeforePack>
     <GenerateNuspecDependsOn>AddNETStandardCompatErrorFileForPackaging;$(GenerateNuspecDependsOn)</GenerateNuspecDependsOn>
   </PropertyGroup>
 

docs/coding-guidelines/adding-api-guidelines.md

@@ -29,12 +29,6 @@ should be added to `net5.0`. [More Information on TargetFrameworks](https://docs
 
 ## Making the changes in repo
 
-**Update pkg**
- - If changing the target framework
-    - Update `SupportedFramework` metadata on the ref ProjectReference to declare the set of concrete platforms you expect your library to support. (see [Specific platform mappings][net-standard table]). Generally will be a combination of netcoreapp2.x, netfx46x, and/or `$(AllXamarinFrameworks)`.
-  - If assembly or package version is updated the package index needs to be updated by running
-    `dotnet build <Library>/pkg/<Library>.pkgproj /t:UpdatePackageIndex`
-
 **Update tests**
   - Add new `TargetFramework` to the ```TargetFrameworks```.
   - Add new test code following [conventions](project-guidelines.md#code-file-naming-conventions) for new files to that are specific to the new target framework.
@@ -52,10 +46,6 @@ Once the dotnet-api-docs change is merged, your comments will start showing up i
 Once the documentation is official, any subsequent updates to it must be made directly in https://github.com/dotnet/dotnet-api-docs/. It's fine to make updates to the triple slash comments later, they just won't automatically flow into the official docs.
 
 ## FAQ
-_**How do I consume APIs from another package that aren't yet published?**_
-
-If you are adding APIs across multiple packages at the same time. You can temporarily add a direct
-ProjectReference from the ref\csproj to the ref\csproj, src\csproj to the ref\csproj, and/or tests\csproj to pkg\pkgproj. Once a new set of packages have been published these ProjectReferences should be removed.
 
 _**What to do if you are moving types down into a lower contract?**_
 

docs/coding-guidelines/libraries-packaging.md

@@ -36,7 +36,7 @@ Removing a library from this transport package is a breaking change and should b
 
 ## NuGet package
 
-Libraries to be packaged must be referenced by the [traversal packaging project](../../src/libraries/libraries-packages.proj) and set `IsPackable` to true. By default, all `Libraries/*/src` projects are considered for packaging.
+Libraries to be packaged must set `IsPackable` to true. By default, all `libraries/*/src` projects are considered for packaging.
 
 Package versions and shipping state should be controlled using the properties defined by the [Arcade SDK](https://github.com/dotnet/arcade/blob/master/Documentation/ArcadeSdk.md#project-properties-defined-by-the-sdk). Typically libraries should not need to explicitly set any of these properties.
 

docs/coding-guidelines/package-projects.md

@@ -151,9 +151,6 @@ All src outputs are under
 
 `bin\$(MSBuildProjectName)\$(TargetFramework)`
 
-## pkg
-In the pkg directory for the library there should be only **one** `.pkgproj` for the primary package for the library. If the library has platform-specific implementations those should be split into platform specific projects in a subfolder for each platform. (see [Package projects](./package-projects.md))
-
 ## tests
 Similar to the src projects tests projects will define a `TargetFrameworks` property so they can list out the set of target frameworks they support.