Fix #28035 Refactor DLL imports interop classes (#48556)

* refactor interop classes

* move interop files to subdirectory

src/libraries/System.IO.Ports/src/Interop/Unix/Interop.Serial.cs → src/libraries/Common/src/Interop/Unix/System.IO.Ports.Native/Interop.Serial.cs

@@ -5,7 +5,6 @@
 using System.IO.Ports;
 using System.Net.Sockets;
 using System.Runtime.InteropServices;
-using Microsoft.Win32.SafeHandles;
 
 internal static partial class Interop
 {

src/libraries/System.IO.Ports/src/Interop/Unix/Interop.Termios.cs → src/libraries/Common/src/Interop/Unix/System.IO.Ports.Native/Interop.Termios.cs

@@ -4,7 +4,6 @@
 using System;
 using System.IO.Ports;
 using System.Runtime.InteropServices;
-using Microsoft.Win32.SafeHandles;
 
 internal static partial class Interop
 {

src/libraries/System.IO.Ports/src/System.IO.Ports.csproj

@@ -120,8 +120,10 @@
   <ItemGroup Condition="'$(TargetsLinux)' == 'true' or '$(TargetsOSX)' == 'true' or '$(TargetsFreeBSD)' == 'true'">
     <Compile Include="System\IO\Ports\SafeSerialDeviceHandle.Unix.cs" />
     <Compile Include="System\IO\Ports\SerialStream.Unix.cs" />
-    <Compile Include="Interop\Unix\Interop.Termios.cs" />
-    <Compile Include="Interop\Unix\Interop.Serial.cs" />
+    <Compile Include="$(CommonPath)Interop\Unix\System.IO.Ports.Native\Interop.Termios.cs"
+             Link="Common\Interop\Unix\System.IO.Ports.Native\Interop.Termios.cs"/>
+    <Compile Include="$(CommonPath)Interop\Unix\System.IO.Ports.Native\Interop.Serial.cs"
+             Link="Common\Interop\Unix\System.IO.Ports.Native\Interop.Serial.cs"/>
     <Compile Include="$(CommonPath)Interop\Unix\Interop.Libraries.cs"
              Link="Common\Interop\Unix\Interop.Libraries.cs" />
     <Compile Include="$(CommonPath)Interop\Unix\Interop.Errors.cs"