Enable per Version DownloadCount for v3 feeds

[campersau]

Bug

Fixes: NuGet/Home#9086
Regression: No

• Last working version: No
• How are we preventing it in future: Added test

Fix

Removing compatibility between v2 and v3 feeds by supporting individual versions counts in v3.
Because the workaround by using the RawSearchResourceV3 directly is now declared obsolete which is currently used in these two places which I know of:

• Add package downloads sample Samples#37
• show download count per version NuGetPackageExplorer/NuGetPackageExplorer#340

Testing/Validation

Tests Added: Yes
Reason for not adding tests:
Validation:

[nkolev92]

Do we understand the implications of this on how the UI behaves?

I like the change, I just want to know what changes.

I'd expect the UI behaves differently when you look at the browse tab. I'd expect the download count for the latest version to be displayed instead of the total.

@chgill-MSFT, I don't know if that's of any concern.

[campersau]

It looks like in VS the DownloadCount from the IPackageSearchMetadata is shown (and not the one from the VersionInfo) so this change should have no impact on that.

NuGet.Client/src/NuGet.Clients/NuGet.PackageManagement.UI/PackageItemLoader.cs

Line 306 in e0d7226

DownloadCount = metadata.DownloadCount,

I also build the VS UI and it showed the same download count as before.

[nkolev92]

Thanks @campersau