Include third-party-notices.txt in all packages

[wtgodbe]

Resolves #20086

Explicitly includes Third-Party-Notices.txt in all packages, and allows packages to use a custom third-party-notices.txt file if they so choose (Identity.UI and the Components packages currently do so). Also includes the version.txt file that was missing from the shared framework

[JunTaoLuo]

Looks good but let's verify the build artifacts when available.

[wtgodbe]

Will do. I took a look at the artifacts on my box & they looked good, but will re-verify w/ the stuff from CI

[dougbu]

How will we keep the Identity/UI and Components files up-to-date @mkArtakMSFT (especially after this change gets into 'master')❔ And, is there a way to automatically verify the files are complete close to release time?

[wtgodbe]

The packages here look correct to me. @safern @ericstj @ViktorHofer does dotnet/runtime do any package testing to validate that files like third-party-notices.txt are actually being included?

[ericstj]

We do some package testing but we don't have tests around those additional files, however we do include them in the dotnet/runtime packages. It wouldn't be difficult to add such a test to our validation.

[ericstj]

Actually, I see we have in our nuget packages, but not in the shared framework. @dagood @NikolaMilosavljevic we might want to fix that.

[dagood]

Installing the .NET Core Runtime places "C:\Program Files\dotnet\ThirdPartyNotices.txt" down alongside the host. Installing it with the sharedfx too might be good for side-by-side installs to get a per-version TPN file, but not sure if it's necessary. @leecow @nakarnam

[dagood]

The goal in the past has seemed to be that "C:\Program Files\dotnet\ThirdPartyNotices.txt" contains data for everything in the directory: dotnet/runtime#3619.