Remove redundant P/Invoke-s in S.D.Process on Apple platforms (#54273)

* Remove P/Invoke to SystemNative_ConfigureTerminalForChildProcess which doesn't exist on Apple platforms

* Address the feedback based on the ifdef approach

* Add IsiOSLike property

* Use a partial method approach

* Address the feedback

src/libraries/System.Diagnostics.Process/src/System.Diagnostics.Process.csproj

@@ -10,6 +10,9 @@
   <PropertyGroup>
     <GeneratePlatformNotSupportedAssemblyMessage Condition="'$(TargetsAnyOS)' == 'true'">SR.Process_PlatformNotSupported</GeneratePlatformNotSupportedAssemblyMessage>
   </PropertyGroup>
+  <PropertyGroup>
+    <IsiOSLike Condition="'$(TargetsMacCatalyst)' == 'true' or '$(TargetsiOS)' == 'true' or '$(TargetstvOS)' == 'true'">true</IsiOSLike>
+  </PropertyGroup>  
   <ItemGroup Condition="'$(TargetsAnyOS)' != 'true'">
     <Compile Include="Microsoft\Win32\SafeHandles\SafeProcessHandle.cs" />
     <Compile Include="System\Collections\Specialized\DictionaryWrapper.cs" />
@@ -234,8 +237,6 @@
              Link="Common\Interop\Unix\Interop.GetHostName.cs" />
     <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.SysConf.cs"
              Link="Common\Interop\Unix\Interop.SysConf.cs" />
-    <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.ConfigureTerminalForChildProcess.cs"
-             Link="Common\Interop\Unix\Interop.ConfigureTerminalForChildProcess.cs" />
     <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.ForkAndExecProcess.cs"
              Link="Common\Interop\Unix\Interop.ForkAndExecProcess.cs" />
     <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.GetGroupList.cs"
@@ -267,6 +268,11 @@
     <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.Access.cs"
              Link="Common\Interop\Unix\System.Native\Interop.Access.cs" />
   </ItemGroup>
+  <ItemGroup Condition=" '$(TargetsUnix)' == 'true' and '$(IsiOSLike)' != 'true'">
+    <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.ConfigureTerminalForChildProcess.cs"
+             Link="Common\Interop\Unix\Interop.ConfigureTerminalForChildProcess.cs" />
+    <Compile Include="System\Diagnostics\Process.Unix.ConfigureTerminalForChildProcesses.cs" />
+  </ItemGroup>
   <ItemGroup Condition=" '$(TargetsLinux)' == 'true'">
     <Compile Include="System\Diagnostics\Process.Linux.cs" />
     <Compile Include="System\Diagnostics\ProcessManager.Linux.cs" />

src/libraries/System.Diagnostics.Process/src/System/Diagnostics/Process.Unix.ConfigureTerminalForChildProcesses.cs

+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Threading;
+
+namespace System.Diagnostics
+{
+    public partial class Process
+    {
+        private static int s_childrenUsingTerminalCount;
+
+        static partial void ConfigureTerminalForChildProcessesInner(int increment)
+        {
+            Debug.Assert(increment != 0);
+
+            int childrenUsingTerminalRemaining = Interlocked.Add(ref s_childrenUsingTerminalCount, increment);
+            if (increment > 0)
+            {
+                Debug.Assert(s_processStartLock.IsReadLockHeld);
+
+                // At least one child is using the terminal.
+                Interop.Sys.ConfigureTerminalForChildProcess(childUsesTerminal: true);
+            }
+            else
+            {
+                Debug.Assert(s_processStartLock.IsWriteLockHeld);
+
+                if (childrenUsingTerminalRemaining == 0)
+                {
+                    // No more children are using the terminal.
+                    Interop.Sys.ConfigureTerminalForChildProcess(childUsesTerminal: false);
+                }
+            }
+        }
+    }
+}

src/libraries/System.Diagnostics.Process/src/System/Diagnostics/Process.Unix.cs

@@ -19,7 +19,6 @@ public partial class Process : IDisposable
         private static volatile bool s_initialized;
         private static readonly object s_initializedGate = new object();
         private static readonly ReaderWriterLockSlim s_processStartLock = new ReaderWriterLockSlim();
-        private static int s_childrenUsingTerminalCount;
 
         /// <summary>
         /// Puts a Process component in state to interact with operating system processes that run in a
@@ -1051,26 +1050,9 @@ private static void OnSigChild(int reapAll)
         /// </summary>
         internal static void ConfigureTerminalForChildProcesses(int increment)
         {
-            Debug.Assert(increment != 0);
-
-            int childrenUsingTerminalRemaining = Interlocked.Add(ref s_childrenUsingTerminalCount, increment);
-            if (increment > 0)
-            {
-                Debug.Assert(s_processStartLock.IsReadLockHeld);
-
-                // At least one child is using the terminal.
-                Interop.Sys.ConfigureTerminalForChildProcess(childUsesTerminal: true);
-            }
-            else
-            {
-                Debug.Assert(s_processStartLock.IsWriteLockHeld);
-
-                if (childrenUsingTerminalRemaining == 0)
-                {
-                    // No more children are using the terminal.
-                    Interop.Sys.ConfigureTerminalForChildProcess(childUsesTerminal: false);
-                }
-            }
+            ConfigureTerminalForChildProcessesInner(increment);
         }
+
+        static partial void ConfigureTerminalForChildProcessesInner(int increment);
     }
 }