Enable StrongName verification in SignCheck

[ellahathaway]

Closes dotnet/source-build#4884

Enable StrongName validation with SignCheck on .NET Core. This PR shares the SN logic from SignTool to SignCheck by moving the logic to a new classlib called Microsoft.DotNet.StrongName and consuming the functionality in SignTool & SignCheck.

Example

Ran SignCheck on https://www.nuget.org/api/v2/package/dotnet-ef/9.0.2. This was the outcome:

<SignCheckResults>
  <File Name="dotnet-ef.9.0.2.nupkg" Outcome="Signed">
    <File Name="dotnet-ef.9.0.2.nupkg/_rels/.rels" Outcome="Skipped" />
    <File Name="dotnet-ef.9.0.2.nupkg/dotnet-ef.nuspec" Outcome="Skipped" />
    <File Name="dotnet-ef.9.0.2.nupkg/Icon.png" Outcome="Skipped" />
    <File Name="dotnet-ef.9.0.2.nupkg/docs/PACKAGE.md" Outcome="Skipped" />
    <File Name="dotnet-ef.9.0.2.nupkg/tools/net8.0/any/DotnetToolSettings.xml" Outcome="Skipped" />
    <File Name="dotnet-ef.9.0.2.nupkg/tools/net8.0/any/shims/win-x64/dotnet-ef.exe" Outcome="Signed" AuthentiCode="Timestamp: 01/17/25 17:31:39 (sha256RSA), AuthentiCode signed: True" StrongName="No StrongName signature (NGEN/CrossGen image)." />
    <File Name="dotnet-ef.9.0.2.nupkg/tools/net8.0/any/dotnet-ef.deps.json" Outcome="Skipped" />
    <File Name="dotnet-ef.9.0.2.nupkg/tools/net8.0/any/ef.runtimeconfig.json" Outcome="Skipped" />
    <File Name="dotnet-ef.9.0.2.nupkg/tools/net8.0/any/shims/win-x86/dotnet-ef.exe" Outcome="Signed" AuthentiCode="Timestamp: 01/17/25 17:31:29 (sha256RSA), AuthentiCode signed: True" StrongName="No StrongName signature (NGEN/CrossGen image)." />
    <File Name="dotnet-ef.9.0.2.nupkg/tools/net8.0/any/dotnet-ef.dll" Outcome="Signed" AuthentiCode="Timestamp: 01/17/25 17:31:29 (sha256RSA), AuthentiCode signed: True" StrongName="StrongName signed: True, Public key = adb9793829ddae60" />
    <File Name="dotnet-ef.9.0.2.nupkg/tools/net8.0/any/dotnet-ef.runtimeconfig.json" Outcome="Skipped" />
    <File Name="dotnet-ef.9.0.2.nupkg/tools/net8.0/any/shims/win-arm64/dotnet-ef.exe" Outcome="Signed" AuthentiCode="Timestamp: 01/17/25 17:31:30 (sha256RSA), AuthentiCode signed: True" StrongName="No StrongName signature (NGEN/CrossGen image)." />
    <File Name="dotnet-ef.9.0.2.nupkg/tools/net8.0/any/dotnet-ef.exe" Outcome="Signed" AuthentiCode="Timestamp: 01/17/25 17:31:30 (sha256RSA), AuthentiCode signed: True" StrongName="No StrongName signature (NGEN/CrossGen image)." />
    <File Name="dotnet-ef.9.0.2.nupkg/tools/net8.0/any/tools/netcoreapp2.0/any/ef.dll" Outcome="Signed" AuthentiCode="Timestamp: 01/17/25 17:32:14 (sha256RSA), AuthentiCode signed: True" StrongName="StrongName signed: True, Public key = adb9793829ddae60" />
    <File Name="dotnet-ef.9.0.2.nupkg/tools/net8.0/any/tools/netcoreapp2.0/any/ef.runtimeconfig.json" Outcome="Skipped" />
    <File Name="dotnet-ef.9.0.2.nupkg/tools/net8.0/any/tools/net472/any/ef.exe" Outcome="Signed" AuthentiCode="Timestamp: 01/17/25 17:33:25 (sha256RSA), AuthentiCode signed: True" StrongName="StrongName signed: True, Public key = adb9793829ddae60" />
    <File Name="dotnet-ef.9.0.2.nupkg/tools/net8.0/any/tools/net472/win-x86/ef.exe" Outcome="Signed" AuthentiCode="Timestamp: 01/17/25 17:31:29 (sha256RSA), AuthentiCode signed: True" StrongName="StrongName signed: True, Public key = adb9793829ddae60" />
    <File Name="dotnet-ef.9.0.2.nupkg/tools/net8.0/any/tools/net472/win-arm64/ef.exe" Outcome="Signed" AuthentiCode="Timestamp: 01/17/25 17:31:29 (sha256RSA), AuthentiCode signed: True" StrongName="StrongName signed: True, Public key = adb9793829ddae60" />
    <File Name="dotnet-ef.9.0.2.nupkg/[Content_Types].xml" Outcome="Skipped" />
    <File Name="dotnet-ef.9.0.2.nupkg/package/services/metadata/core-properties/a812c08dbe0b4e168df2a9a030bdf821.psmdcp" Outcome="Skipped" />
    <File Name="dotnet-ef.9.0.2.nupkg/.signature.p7s" Outcome="Skipped" />
  </File>
</SignCheckResults>

Token info validated manually with sn:

sn -T dotnet-ef.dll 
Mono StrongName - version 6.8.0.105
StrongName utility for signing assemblies
Copyright 2002, 2003 Motus Technologies. Copyright 2004-2008 Novell. BSD licensed.

Public Key Token: adb9793829ddae60

[ellahathaway]

https://dev.azure.com/dnceng/internal/_build/results?buildId=2657811&view=results

The pipeline results are correct. I pulled assemblies that are strongnamed and not strongnamed and validated the SignCheck output manually.