Adding Framework 4.8.1 and .NET8 to targets.

This required platform-specific references in the project files. I also fixed a warning about Assembly.CodeBase and some .NET8 warnings about manually copying duplicate files into our nuget package folder when packing. These files appear to be duplicates of what is copied during the .NET8 packaging.

Directory.Build.props

@@ -1,6 +1,6 @@
 <Project>
   <PropertyGroup>
-    <TargetFrameworks>net461</TargetFrameworks>
+    <TargetFrameworks>net461;net481;net8.0-windows</TargetFrameworks>
     <Company>SIL</Company>
     <Authors>SIL International</Authors>
     <Product>L10NSharp</Product>
@@ -24,6 +24,7 @@ See full changelog at https://github.com/sillsdev/l10nsharp/blob/master/CHANGELO
     </AppendToReleaseNotesProperty>
     <GeneratePackageOnBuild>true</GeneratePackageOnBuild>
     <GenerateResourceUsePreserializedResources>true</GenerateResourceUsePreserializedResources>
+    <UseWindowsForms>true</UseWindowsForms>
   </PropertyGroup>
   <ItemGroup>
     <!-- Without this line some projects fail to build on TC with "error : SourceRoot items

src/CheckOrFixXliff/CheckOrFixXliff.csproj

@@ -9,9 +9,9 @@
     <PackageLicenseExpression>MIT</PackageLicenseExpression>
     <PackageProjectUrl>https://github.com/sillsdev/l10nsharp/tree/master/src/CheckOrFixXliff</PackageProjectUrl>
     <TargetsForTfmSpecificBuildOutput>$(TargetsForTfmSpecificBuildOutput);CopyProjectReferencesToPackage</TargetsForTfmSpecificBuildOutput>
-    <NoWarn>$(NoWarn);NU5128</NoWarn>
+    <NoWarn>$(NoWarn);NU5128;NU5118</NoWarn>
   </PropertyGroup>
-  <ItemGroup>
+  <ItemGroup Condition=" '$(TargetFramework)' == 'net461' Or '$(TargetFramework)' == 'net481' ">
     <Reference Include="System.ServiceModel" />
     <Reference Include="System.Windows.Forms" />
   </ItemGroup>

src/CheckOrFixXliff/Program.cs

@@ -176,7 +176,7 @@ private static bool CheckForWellFormedXml(string filename)
 		private static bool ValidateXliffAgainstSchema(string filename)
 		{
 			bool valid = true;
-			var installedXliffDir = Path.GetDirectoryName(new Uri(Assembly.GetExecutingAssembly().CodeBase).LocalPath);
+			var installedXliffDir = Path.GetDirectoryName(new Uri(Assembly.GetExecutingAssembly().Location).LocalPath);
 			var schemaLocation = Path.Combine(installedXliffDir, "xliff-core-1.2-transitional.xsd");
 			var schemas = new XmlSchemaSet();
 			using (var reader = XmlReader.Create(schemaLocation))

src/ExtractXliff/ExtractXliff.csproj

@@ -9,9 +9,9 @@
     <PackageId>L10NSharp.ExtractXliff</PackageId>
     <PackageProjectUrl>https://github.com/sillsdev/l10nsharp/tree/master/src/ExtractXliff</PackageProjectUrl>
     <TargetsForTfmSpecificBuildOutput>$(TargetsForTfmSpecificBuildOutput);CopyProjectReferencesToPackage</TargetsForTfmSpecificBuildOutput>
-    <NoWarn>$(NoWarn);NU5128</NoWarn>
+    <NoWarn>$(NoWarn);NU5128;NU5118</NoWarn>
   </PropertyGroup>
-  <ItemGroup>
+  <ItemGroup Condition=" '$(TargetFramework)' == 'net461' Or '$(TargetFramework)' == 'net481' ">
     <Reference Include="System.ServiceModel" />
     <Reference Include="System.Windows.Forms" />
   </ItemGroup>

src/L10NSharp/L10NSharp.csproj

@@ -1,19 +1,27 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <RootNamespace>L10NSharp</RootNamespace>
     <Description>L10NSharp is a .NET localization library for Windows Forms applications. It collects strings which need localization when your application first runs and saves them in a XLIFF file. It can also dynamically collect strings at runtime.</Description>
     <AssemblyTitle>L10NSharp</AssemblyTitle>
     <PackageId>L10NSharp</PackageId>
     <PackageProjectUrl>https://github.com/sillsdev/l10nsharp</PackageProjectUrl>
   </PropertyGroup>
-  <ItemGroup>
+  <ItemGroup Condition=" '$(TargetFramework)' == 'net461' Or '$(TargetFramework)' == 'net481' ">
     <Reference Include="System.ServiceModel" />
     <Reference Include="System.Windows.Forms" />
   </ItemGroup>
-  <ItemGroup>
+  <ItemGroup Condition=" '$(TargetFramework)' == 'net461' Or '$(TargetFramework)' == 'net481' ">
     <PackageReference Include="GitVersion.MsBuild" Version="5.11.1" PrivateAssets="all" />
     <PackageReference Include="Microsoft.SourceLink.GitHub" Version="1.1.1" PrivateAssets="all" />
     <PackageReference Include="SIL.ReleaseTasks" Version="2.5.0" PrivateAssets="all" />
     <PackageReference Include="System.Resources.Extensions" Version="6.0.0" />
   </ItemGroup>
+  <ItemGroup Condition=" '$(TargetFramework)' == 'net8.0-windows' ">
+    <PackageReference Include="GitVersion.MsBuild" Version="5.11.1" PrivateAssets="all" />
+    <PackageReference Include="Microsoft.SourceLink.GitHub" Version="1.1.1" PrivateAssets="all" />
+    <PackageReference Include="SIL.ReleaseTasks" Version="2.5.0" PrivateAssets="all" />
+    <PackageReference Include="System.Resources.Extensions" Version="6.0.0" />
+    <PackageReference Include="System.ServiceModel.Http" Version="6.2.0" />
+    <PackageReference Include="System.ServiceModel.Primitives" Version="6.2.0" />
+  </ItemGroup>
 </Project>

src/L10NSharpTests/L10NSharpTests.csproj

@@ -11,9 +11,9 @@
 	<ItemGroup>
 	  <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.4.0" />
 	  <PackageReference Include="NUnit" Version="3.13.3" />
-	  <PackageReference Include="NUnit3TestAdapter" Version="4.3.1" />
+	  <PackageReference Include="NUnit3TestAdapter" Version="4.5.0" />
 	</ItemGroup>
-	<ItemGroup>
+	<ItemGroup Condition=" '$(TargetFramework)' == 'net461' Or '$(TargetFramework)' == 'net481' ">
 	  <Reference Include="System.Windows.Forms" />
 	</ItemGroup>
 </Project>

src/SampleApp/SampleApp.csproj

@@ -5,7 +5,7 @@
     <AssemblyTitle>SampleApp</AssemblyTitle>
     <IsPackable>false</IsPackable>
   </PropertyGroup>
-  <ItemGroup>
+  <ItemGroup Condition=" '$(TargetFramework)' == 'net461' Or '$(TargetFramework)' == 'net481' ">
     <Reference Include="System.Windows.Forms" />
   </ItemGroup>
   <ItemGroup>