Run the template commands (dotnet tool t4) only once (#184)

* Run the template commands (dotnet tool t4) only once.
Otherwise, the commands would be run for each target framework, which sometimes could cause file lock errors (and degrades performance).

This is based on this StackOverflow answer: https://stackoverflow.com/questions/50071932/how-do-i-call-my-script-before-all-the-builds-for-only-once-in-a-multi-targeting/50080946#50080946

* Follow-Up: Add comment.

Author: kpreisser

src/Wasmtime.csproj

@@ -68,11 +68,11 @@ The .NET embedding of Wasmtime enables .NET code to instantiate WebAssembly modu
     <Service Include="{508349b6-6b84-4df5-91f0-309beebad82d}" />
   </ItemGroup>
 
-  <Target Name="RestoreTools" BeforeTargets="BeforeBuild">
+  <Target Name="RunCodeTemplates" BeforeTargets="DispatchToInnerBuilds">
+    <!-- Generate the code files from the T4 text templates.
+         We use the "DispatchToInnerBuilds" target so that they are only run once when
+         building the project, instead of for each target framework. -->
     <Exec Command="dotnet tool restore" />
-  </Target>
-
-  <Target Name="RunCodeTemplates" BeforeTargets="BeforeBuild">
     <Exec Command="dotnet tool run t4 Linker.DefineFunction.tt" />
     <Exec Command="dotnet tool run t4 Function.FromCallback.tt" />
   </Target>