How to `extern alias` an assembly with .Net core?

I believe the issue you are trying to link to is here:
https://github.com/NuGet/Home/issues/4989

You can workaround by using an MSBuild Target. drop this snippet into Directory.Build.targets:

<Target Name="AddPackageAliases" BeforeTargets="ResolveReferences" Outputs="%(PackageReference.Identity)">
    <PropertyGroup>
        <AliasPackageReference>@(PackageReference->'%(Identity)')</AliasPackageReference>
        <AliasName>@(PackageReference->'%(Alias)')</AliasName>
    </PropertyGroup>

    <ItemGroup>
        <ReferencePath Condition="'%(FileName)'=='$(AliasPackageReference)'">
            <Aliases>$(AliasName)</Aliases>
        </ReferencePath>
    </ItemGroup>
</Target>

and then use it in your csproj in your PackageReference nodes like this:

<ItemGroup>
    <PackageReference Include="StackExchange.Redis.StrongName" Version="1.2.6" Alias="signed" />
</ItemGroup>

added this as a comment to the GitHub issue:
https://github.com/NuGet/Home/issues/4989#issuecomment-426666530

I had a problem in .Net Core 2.2 where the MySqlConnector type name and namespace had a collision and the answer was to create an alias. I think this should work for your needs too, just change MySqlConnector below accordingly: https://stackoverflow.com/a/48686823/479701

<Target Name="ChangeAliasesOfStrongNameAssemblies" BeforeTargets="FindReferenceAssembliesForReferences;ResolveReferences">
    <ItemGroup>
      <ReferencePath Condition="'%(FileName)' == 'MySqlConnector'">
        <Aliases>MySqlConnectorAlias</Aliases>
      </ReferencePath>
    </ItemGroup>
  </Target>

then in your cs file before usings:

extern alias MySqlConnectorAlias;

then reference your type like this:

MySqlConnectorAlias::MySql.Data.MySqlClient.MySqlConnection