Use snupkg instead of embedded symbols (#1916)

Rx.NET/Source/Directory.build.props

@@ -7,7 +7,6 @@
     <PackageIconUrl>https://raw.githubusercontent.com/dotnet/reactive/0f837d11385cfaf575861ccc5a5fbcafb22d888f/Rx.NET/Resources/Artwork/Logo.png</PackageIconUrl>
     <PackageProjectUrl>https://github.com/dotnet/reactive</PackageProjectUrl>
     <PackageLicenseExpression>MIT</PackageLicenseExpression>
-    <DebugType Condition="'$(Configuration)' != 'Debug'">embedded</DebugType>
     <SignAssembly>true</SignAssembly>
     <AssemblyOriginatorKeyFile>$(MSBuildThisFileDirectory)ReactiveX.snk</AssemblyOriginatorKeyFile>
     <NoWarn>$(NoWarn);1701;1702;CS1591;NU5105</NoWarn>
@@ -26,6 +25,11 @@
     <NoWarn>$(NoWarn);CS8600;CS8602;CS8603;CS8604;CS8632;CA1000;CA1003;CA1014;CA1019;CA1033;CA1045;CA1051;CA1052;CA1063;CA1067;CA1068;CA1507;CA1707;CA1711;CA1716;CA1720;CA1806;CA1815;CA1816;CA1822;CA1825;CA1840;CA1845;CA2016;CA2109;CA2201;CA2211;CA2213;CA2249;IDE0003;IDE0016;IDE0017;IDE0018;IDE0019;IDE0020;IDE0031;IDE0032;IDE0034;IDE0037;IDE0038;IDE0039;IDE0040;IDE0044;IDE0051;IDE0052;IDE0056;IDE0057;IDE0059;IDE0060;IDE0062;IDE0063;IDE0071;IDE0074;IDE0075;IDE0076;IDE0077;IDE0079;IDE0083;IDE0090;IDE0180;IDE0270;IDE0280;IDE1006;IDE1056</NoWarn>
   </PropertyGroup>
 
+  <PropertyGroup Condition="'$(Configuration)' != 'Debug'">
+    <IncludeSymbols>true</IncludeSymbols>
+    <SymbolPackageFormat>snupkg</SymbolPackageFormat>    
+  </PropertyGroup>
+
   <PropertyGroup Condition="'$(TF_BUILD)' == 'true'">
     <ContinuousIntegrationBuild>true</ContinuousIntegrationBuild>
   </PropertyGroup>