Targeting netstandard 2.1 for more projects

[agr]

Internal projects targeting .net depend on those packages and produce build warnings because of unsupported targets. Nothing really prevents those from targeting netstandard 2.1 (not netstandard2.0 because of EF).

Had to apply a fix to Validation DB's EntitiesConfiguration similar to what we have for Gallery DB:

NuGetGallery/src/NuGetGallery.Core/Entities/EntitiesConfiguration.cs

Lines 7 to 43 in febd3fb

	#if NETFRAMEWORK
	using System.Runtime.Remoting.Messaging;
	#endif
	namespace NuGetGallery
	{
	public class EntitiesConfiguration
	: DbConfiguration
	{
	#if NETFRAMEWORK
	public EntitiesConfiguration()
	{
	// Configure Connection Resiliency / Retry Logic
	// See https://msdn.microsoft.com/en-us/data/dn456835.aspx and msdn.microsoft.com/en-us/data/dn307226
	SetExecutionStrategy("System.Data.SqlClient", () => SuspendExecutionStrategy
	? (IDbExecutionStrategy)new DefaultExecutionStrategy() : new SqlAzureExecutionStrategy());
	}
	public static bool SuspendExecutionStrategy
	{
	get
	{
	return (bool?)CallContext.LogicalGetData("SuspendExecutionStrategy") ?? false;
	}
	set
	{
	CallContext.LogicalSetData("SuspendExecutionStrategy", value);
	}
	}
	#else
	public EntitiesConfiguration()
	{
	// Configure Connection Resiliency / Retry Logic
	// See https://msdn.microsoft.com/en-us/data/dn456835.aspx and msdn.microsoft.com/en-us/data/dn307226
	SetExecutionStrategy("System.Data.SqlClient", () => new SqlAzureExecutionStrategy());
	}
	#endif

Functionally, there are no changes for projects consuming those that target net472 and projects targeting .net can actually now use those.

[erdembayar]

@agr
Please add related issue link if you have one?