Convert projects in this repo to use ProjectReference

[natemcmaster]

Follow-up to #3598.

The first phase of reducing repos was to merge the source code into a single repo. The second phase is to convert them from isolated folders of code with PackageReference across repo boundaries, to projects which use ProjectReference.

We've already started some of this work. See #4013 for example and https://github.com/aspnet/AspNetCore/tree/master/src/DataProtection.

As done in #4013, we implement this using <Reference> items in .csproj and custom Reference resolution targets. This is done so we can automatically pick the right versions of assemblies to used based on conditions such as, is this a test project? is this branch building a patch or a new minor release? what versions were used in the last stable release? etc.

See also https://github.com/aspnet/specs/blob/master/runtime/design-notes/2018-10-03-mondo-source-org.md for the spec on source code organization.

Repo groups to convert

• Razor @ajaybhargavb
• HttpSysServer Make HttpSys use ProjectReference and move HttpSys into Servers folder #4335
• Antiforgery - Justin
• IISIntegration Make IISIntegration use Reference instead of PackageReference (and reactionary work) #4311
• CORS - Justin
• StaticFiles - Justin
• Routing @natemcmaster
• ResponseCaching -Justin
• Session @JunTaoLuo
• ServerTests @JunTaoLuo @jkotalik
• Localization @natemcmaster
• Security @jkotalik
• MetaPackages @JunTaoLuo
• Mvc @ajaybhargavb
• JavaScriptServices @jkotalik
• AADIntegration @natemcmaster
• Identity @JunTaoLuo
• MvcPrecompilation @JunTaoLuo
• AzureIntegration @natemcmaster
• SignalR @natemcmaster
• Components @natemcmaster
• MusicStore @jkotalik
• AuthSamples @jkotalik
• Templating @natemcmaster

[natemcmaster]

cc @jkotalik who is helping do this for src/IISIntegration/

[jkotalik]

Once I get this done for IISIntegration, I'll do other repos too. IISIntegration was significantly more difficult to port than other repos (due to native dependencies).

[natemcmaster]

I'm adding a checklist to the original issue to track the groups of subrepos that we need to convert. Let's start by doing these one at a time.