Microsoft.CodeDom.Providers.DotNetCompilerPlatform should use the latest version dependant on the target framework version

[CZEMacLeod]

The package Microsoft.CodeDom.Providers.DotNetCompilerPlatform now has versions 3.11.0 and 4.1.0 released.
The SDK should use the new version where possible.
If the TargetFramework is net472 or higher we can use 4.1.0. For net462 or higher we can use 3.11.0.
If we are trying to target older than net462 (up to net45) we need to keep on the current 3.6.0 version.

[CZEMacLeod]

This may need to be reworked based on the work in #56 and #54.

  <ItemGroup>
    <_SDKPackageReference Update="Microsoft.CodeDom.Providers.DotNetCompilerPlatform"
                          SDKDefaultVersion="3.11.0"
                          Condition="$([System.Version]::Parse('$(TargetFrameworkVersion.Substring(1))').CompareTo($([System.Version]::Parse('4.6.2')))) &gt;= 0" />
    <_SDKPackageReference Update="Microsoft.CodeDom.Providers.DotNetCompilerPlatform"
                          SDKDefaultVersion="4.1.0"
                          Condition="$([System.Version]::Parse('$(TargetFrameworkVersion.Substring(1))').CompareTo($([System.Version]::Parse('4.7.2')))) &gt;= 0" />
  </ItemGroup>