experiment: multi-assembly package

[EronWright]

A prototype, to be incorporated into code generation tooling.

This PR refactors the Pulumi.AzureNative assembly into a set of assemblies, bundled together into a Pulumi.AzureNative nuget package. The expected benefit is improved build time for the provider SDK, and possibly improved efficiency at runtime.

No impact is expected to consumer projects, they continue to use a <PackageReference> as normal. All assemblies in the package are included into the project's compile dependencies.

The package contents resemble:

❯ tar -tf bin/Debug/Pulumi.AzureNative.2.0.0-alpha.0.nupkg
_rels/.rels
Pulumi.AzureNative.nuspec
lib/net6.0/Pulumi.AzureNative.Common.dll
lib/net6.0/Pulumi.AzureNative.Aad.dll
lib/net6.0/Pulumi.AzureNative.AadIam.dll
lib/net6.0/Pulumi.AzureNative.Addons.dll
...
lib/net6.0/Pulumi.AzureNative.WindowsESU.dll
lib/net6.0/Pulumi.AzureNative.WindowsIoT.dll
lib/net6.0/Pulumi.AzureNative.Workloads.dll
lib/net6.0/Pulumi.AzureNative.Common.xml
lib/net6.0/Pulumi.AzureNative.Aad.xml
lib/net6.0/Pulumi.AzureNative.AadIam.xml
lib/net6.0/Pulumi.AzureNative.Addons.xml
...
lib/net6.0/Pulumi.AzureNative.WindowsESU.xml
lib/net6.0/Pulumi.AzureNative.WindowsIoT.xml
lib/net6.0/Pulumi.AzureNative.Workloads.xml
content/version.txt
content/pulumi-plugin.json
logo.png
[Content_Types].xml
package/services/metadata/core-properties/ef56176ce1ce46809ab6450086a172fa.psmdcp

To build and install locally:

$ cd sdk/dotnet
$ dotnet pack Pulumi.AzureNative.csproj
$ nuget init bin/Debug bin/Debug/feed/
$ dotnet nuget locals global-packages --clear

See also: NuGet/Home#3891 (comment)

[github-actions]

Does the PR have any schema changes?

Looking good! No breaking changes found.
No new resources/functions.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 56.80%. Comparing base (ee72d75) to head (00740f0).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3746   +/-   ##
=======================================
  Coverage   56.80%   56.80%           
=======================================
  Files          74       74           
  Lines       11838    11838           
=======================================
+ Hits         6724     6725    +1     
+ Misses       4619     4618    -1     
  Partials      495      495           

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