Update the sample to target net5 (#4096)

* Update the sample to target netcoreapp3.1

It generates warnings because it targets out-of-support 3.0

* Update to .NET 5

The CI seems to only support .NET 5 and it doesn't really matter for the sample if it's 3.1 or 5.

* Update readme accordingly

core/extensions/AppWithPlugin/AppWithPlugin/AppWithPlugin.csproj

@@ -2,7 +2,7 @@
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFramework>netcoreapp3.0</TargetFramework>
+    <TargetFramework>net5</TargetFramework>
   </PropertyGroup>
 
   <ItemGroup>

core/extensions/AppWithPlugin/AppWithPlugin/Program.cs

@@ -21,12 +21,12 @@ static void Main(string[] args)
 
                 string[] pluginPaths = new string[]
                 {
-                    @"HelloPlugin\bin\Debug\netcoreapp3.0\HelloPlugin.dll",
-                    @"JsonPlugin\bin\Debug\netcoreapp3.0\JsonPlugin.dll",
-                    @"XcopyablePlugin\bin\Debug\netcoreapp3.0\XcopyablePlugin.dll",
-                    @"OldJsonPlugin\bin\Debug\netcoreapp2.1\OldJsonPlugin.dll",
-                    @"FrenchPlugin\bin\Debug\netcoreapp2.1\FrenchPlugin.dll",
-                    @"UVPlugin\bin\Debug\netcoreapp2.1\UVPlugin.dll",
+                    @"HelloPlugin\bin\Debug\net5\HelloPlugin.dll",
+                    @"JsonPlugin\bin\Debug\net5\JsonPlugin.dll",
+                    @"XcopyablePlugin\bin\Debug\net5\XcopyablePlugin.dll",
+                    @"OldJsonPlugin\bin\Debug\net5\OldJsonPlugin.dll",
+                    @"FrenchPlugin\bin\Debug\net5\FrenchPlugin.dll",
+                    @"UVPlugin\bin\Debug\net5\UVPlugin.dll",
                 };
 
                 IEnumerable<ICommand> commands = pluginPaths.SelectMany(pluginPath =>

core/extensions/AppWithPlugin/FrenchPlugin/FrenchPlugin.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>netcoreapp2.1</TargetFramework>
+    <TargetFramework>net5</TargetFramework>
   </PropertyGroup>
 
   <ItemGroup>

core/extensions/AppWithPlugin/HelloPlugin/HelloPlugin.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>netcoreapp3.0</TargetFramework>
+    <TargetFramework>net5</TargetFramework>
   </PropertyGroup>
 
   <ItemGroup>

core/extensions/AppWithPlugin/JsonPlugin/JsonPlugin.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>netcoreapp3.0</TargetFramework>
+    <TargetFramework>net5</TargetFramework>
   </PropertyGroup>
 
   <ItemGroup>

core/extensions/AppWithPlugin/OldJsonPlugin/OldJsonPlugin.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>netcoreapp2.1</TargetFramework>
+    <TargetFramework>net5</TargetFramework>
   </PropertyGroup>
 
   <ItemGroup>

core/extensions/AppWithPlugin/PluginBase/PluginBase.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>netcoreapp2.1</TargetFramework>
+    <TargetFramework>net5</TargetFramework>
   </PropertyGroup>
 
 </Project>

core/extensions/AppWithPlugin/ReadMe.md

@@ -10,8 +10,8 @@ By using `AssemblyDependencyResolver` along with a custom `AssemblyLoadContext`,
 
 ## Build and Run
 
-1. Install .NET Core 3.0 Preview 2 or newer.
-2. Use the .NET Core SDK to build the project via `dotnet build`.
+1. Install .NET 5 or newer. The sample targets .NET 5, but support for all the features it uses was added in .NET Core 3.0.
+2. Use the .NET SDK to build the project via `dotnet build`.
    - The AppWithPlugin project does not contain any references to the plugin projects, so you need to build the solution.
 3. Go to the AppWithPlugin directory and use `dotnet run` to run the app.
     - You should see the app output a list of installed commands.

core/extensions/AppWithPlugin/UVPlugin/UVPlugin.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>netcoreapp2.1</TargetFramework>
+    <TargetFramework>net5</TargetFramework>
   </PropertyGroup>
 
   <ItemGroup>

core/extensions/AppWithPlugin/XcopyablePlugin/XcopyablePlugin.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>netcoreapp3.0</TargetFramework>
+    <TargetFramework>net5</TargetFramework>
     <CopyLocalLockFileAssemblies>true</CopyLocalLockFileAssemblies>
   </PropertyGroup>