[build] Copy Mono.Options.pdb to output directory (#896)

Context: https://devdiv.visualstudio.com/DevDiv/_workitems/edit/1421424/

A recent update to `Mono.Options.dll` (presumably commit c936d09)
has caused a symbol check failure in our latest VS insertion.  We can
fix this by updating one of the tools projects that references this
package to copy `Mono.Options.pdb` to the Output Directory.

Once the file is in the right output path we can include it in the
Xamarin.Android installers.

Author: pjcollins

tools/generator/generator.csproj

@@ -31,7 +31,7 @@
 
   <ItemGroup>
     <PackageReference Include="Irony" />
-    <PackageReference Include="Mono.Options" />
+    <PackageReference Include="Mono.Options" GeneratePathProperty="true" />
     <!-- Since we are sharing an OutputDirectory, and HtmlAgilityPack is also referenced by a different netstandard2.0 libary,
           we can explicitly reference the netstandard2.0 version here. This will also ensure symbol files are copied to the output directory. -->
     <PackageReference Include="HtmlAgilityPack" ExcludeAssets="Compile" GeneratePathProperty="true" />
@@ -41,6 +41,11 @@
     <PackageReference Include="Microsoft.NETFramework.ReferenceAssemblies" PrivateAssets="All" />
   </ItemGroup>
 
+  <ItemGroup>
+    <None Condition=" '$(TargetFramework)' == 'net472' " Include="$(PkgMono_Options)\lib\net40\Mono.Options.pdb" CopyToOutputDirectory="PreserveNewest" />
+    <None Condition=" '$(TargetFramework)' == 'net6.0' " Include="$(PkgMono_Options)\lib\netstandard2.0\Mono.Options.pdb" CopyToOutputDirectory="PreserveNewest" />
+  </ItemGroup>
+
   <ItemGroup>
     <ProjectReference Include="..\..\src\Java.Interop.Localization\Java.Interop.Localization.csproj" />
     <ProjectReference Include="..\..\src\Java.Interop.Tools.Generator\Java.Interop.Tools.Generator.csproj" />