Merge pull request #5 from Gearset/dotnet9

Add .net6/7/8/9 support, remove netstandard2.0

Author: daverant

global.json

@@ -0,0 +1,7 @@
+{
+  "sdk": {
+    "version": "9.0.0",
+    "rollForward": "latestMajor",
+    "allowPrerelease": false
+  }
+}

src/itextsharp.csproj

@@ -5,7 +5,7 @@
     <DefaultClientScript>JScript</DefaultClientScript>
     <DefaultHTMLPageLayout>Grid</DefaultHTMLPageLayout>
     <DefaultTargetSchema>IE50</DefaultTargetSchema>
-    <TargetFramework>netstandard2.0</TargetFramework>
+    <TargetFrameworks>net6.0;net7.0;net8.0;net9.0;</TargetFrameworks>
     <AssemblyTitle>iTextSharp</AssemblyTitle>
     <Description>iTextSharp 4.1.6 with added support for tables and images</Description>
     <Copyright>Copyright (C) 1999-2009 by Bruno Lowagie and Paulo Soares. All Rights Reserved.</Copyright>

tests/itextsharp.Tests/itextsharp.Tests.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
     <PropertyGroup>
-        <TargetFramework>netcoreapp2.1</TargetFramework>
+        <TargetFramework>net9.0</TargetFramework>
 
         <IsPackable>false</IsPackable>
     </PropertyGroup>