add net472 target so that we get optimized IndexOf on those platforms where it should work

Directory.Build.props

@@ -4,8 +4,7 @@
     <Copyright>2017 Stack Exchange, Inc.</Copyright>
     <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
     <GenerateDocumentationFile>true</GenerateDocumentationFile>
-    <LibTargetFrameworks Condition="'$(OS)' == 'Windows_NT'">net461;netstandard2.0</LibTargetFrameworks>
-    <LibTargetFrameworks Condition="'$(OS)' != 'Windows_NT'">netstandard2.0</LibTargetFrameworks>
+    <LibTargetFrameworks>netstandard2.0</LibTargetFrameworks>
     <AssemblyOriginatorKeyFile>$(MSBuildThisFileDirectory)StackExchange.Redis.snk</AssemblyOriginatorKeyFile>
     <PackageId>$(AssemblyName)</PackageId>
     <Features>strict</Features>

src/StackExchange.Redis/StackExchange.Redis.csproj

 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
+    <!-- extend the default lib targets for the main lib; mostly because of "vectors" -->
+    <LibTargetFrameworks Condition="'$(OS)' == 'Windows_NT'">net461;netstandard2.0;net472</LibTargetFrameworks>
     <TargetFrameworks>$(LibTargetFrameworks)</TargetFrameworks>
     <Description>High performance Redis client, incorporating both synchronous and asynchronous usage.</Description>
     <AssemblyName>StackExchange.Redis</AssemblyName>
@@ -17,7 +19,7 @@
     <PackageReference Include="System.Diagnostics.PerformanceCounter" Version="4.5.0" />
     <PackageReference Include="System.IO.Pipelines" Version="4.5.0" />
     <PackageReference Include="System.Threading.Channels" Version="4.5.0" />
-    <!-- net472 needs this for ZipArchive; I have no idea why this changed, but... meh -->
+    <!-- net472 needs this for ZipArchive; I have no idea why this changed, but... meh; note this also demands SDK 2.1.400 -->
     <PackageReference Include="System.IO.Compression" Version="4.3.0" Condition="'$(TargetFramework)' == 'net472'" />
   </ItemGroup>
 </Project>
\ No newline at end of file

toys/TestConsole/TestConsole.csproj

@@ -2,7 +2,7 @@
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFrameworks>netcoreapp2.1;net462;net47</TargetFrameworks>
+    <TargetFrameworks>netcoreapp2.1;net462;net47;net472</TargetFrameworks>
     <LangVersion>latest</LangVersion>
   </PropertyGroup>