Reduce target framework matrix to netstandard2.0;net47;net10.0

Drops 8 EOL or redundant TFMs (netcoreapp3.0, netcoreapp3.1, net5.0, net6.0,
net7.0, net8.0, net471, net472, net48, net481). Coverage is preserved:
netstandard2.0 covers all modern .NET (5+), net47 keeps the SetDllDirectory
bootstrap available for .NET Framework consumers, and net10.0 is the current
LTS modern-.NET target.

Broadens #if NET472_OR_GREATER to #if NETFRAMEWORK in NativeMethods.cs so the
SetDllDirectory bootstrap compiles into the net47 build (previously the gate
was narrower than the TFM list).

Author: timyhac

src/libplctag.NativeImport/NativeMethods.cs

@@ -20,7 +20,7 @@ static class NativeMethods
 
         static NativeMethods()
         {
-#if NET472_OR_GREATER
+#if NETFRAMEWORK
             // Assume we're running on Windows because .NET Framework is not supported on other platforms
             string executingDirectory = System.IO.Path.GetDirectoryName(typeof(NativeMethods).Assembly.Location);
 			string system = Environment.Is64BitProcess ? "X64" : "X86";

src/libplctag.NativeImport/libplctag.NativeImport.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>netcoreapp3.0;netcoreapp3.1;net5.0;net6.0;net7.0;net8.0;net47;net471;net472;net48;net481</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net47;net10.0</TargetFrameworks>
     <AssemblyName>libplctag.NativeImport</AssemblyName>
     <RootNamespace>libplctag.NativeImport</RootNamespace>
     <PackageId>libplctag.NativeImport</PackageId>

src/libplctag/libplctag.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>netcoreapp3.0;netcoreapp3.1;net5.0;net6.0;net7.0;net8.0;net47;net471;net472;net48;net481</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net47;net10.0</TargetFrameworks>
     <AssemblyName>libplctag</AssemblyName>
     <RootNamespace>libplctag</RootNamespace>
     <PackageId>libplctag</PackageId>