Switch to build-time generation for Resx Files

[eerhardt]

When using our default .csproj template:

  <ItemGroup>
    <Compile Include="**\*.cs" Exclude="$(GlobalExclude)" />
    <EmbeddedResource Include="**\*.resx" Exclude="$(GlobalExclude)" />
    <None Include="project.json" />
  </ItemGroup>

We don't get the ResXFileCodeGenerator executed, so there isn't a nice developer experience of how to get access to the resources.

/cc @davkean @srivatsn @natidea @nguerrera

[nguerrera]

We want to make this happen in the build and emit code to the obj\ directory. I believe we will need to reimplement the strongly-typed resource generator to be xplat and not depend on CodeDom.

[srivatsn]

We should make the template work for RC2 with the current system and then investigate moving to generation during build afterwards.

[nguerrera]

Adding a new resx in VS after newing up from template results in this:

<Project Sdk="Microsoft.NET.Sdk" ToolsVersion="15.0">
  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>netcoreapp1.0</TargetFramework>
  </PropertyGroup>
  <ItemGroup>
    <Compile Include="**\*.cs" />
    <EmbeddedResource Include="**\*.resx" />
  </ItemGroup>
  <ItemGroup>
    <PackageReference Include="Microsoft.NETCore.App" Version="1.0.1" />
  </ItemGroup>
  <ItemGroup>
    <Compile Update="Resource1.Designer.cs">
      <DesignTime>True</DesignTime>
      <AutoGen>True</AutoGen>
      <DependentUpon>Resource1.resx</DependentUpon>
    </Compile>
  </ItemGroup>
  <ItemGroup>
    <EmbeddedResource Update="Resource1.resx">
      <Generator>ResXFileCodeGenerator</Generator>
      <LastGenOutput>Resource1.Designer.cs</LastGenOutput>
    </EmbeddedResource>
  </ItemGroup>
</Project>

We should do the build-time generation for xplat (and get a more concise csproj), but the template is not blocking the VS experience.

However, dotnet/project-system#747 is blocking the experience.