Exclude the managed code around libproc on iOS/tvOS (dotnet#61590)

Since libproc is a private Apple API, it is not available on iOS/tvOS and should be excluded (see dotnet#61265 (comment) and above for more details).  
This PR excludes $(CommonPath)Interop\OSX\Interop.libproc.cs on the iOS/tvOS as well as makes some methods in Process, ProcessManager, and ProcessThread classes calling that API throw PNSE so that for iOS/tvOS it's possible to re-use the respective *.UnknownUnix.cs parts.

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

@@ -5,7 +5,7 @@
     <TargetFrameworks>$(NetCoreAppCurrent)-windows;$(NetCoreAppCurrent)-FreeBSD;$(NetCoreAppCurrent)-Linux;$(NetCoreAppCurrent);$(NetCoreAppCurrent)-OSX;$(NetCoreAppCurrent)-iOS;$(NetCoreAppCurrent)-tvOS</TargetFrameworks>
     <Nullable>enable</Nullable>
     <!-- Suppress unused field warnings when using PlatformNotSupportedException stubs -->
-    <NoWarn Condition=" '$(TargetsFreeBSD)' == 'true' or '$(TargetsUnknownUnix)' == 'true' ">$(NoWarn);0649</NoWarn>
+    <NoWarn Condition=" '$(TargetsFreeBSD)' == 'true' or '$(TargetsUnknownUnix)' == 'true' or '$(TargetsiOS)' == 'true' or '$(TargetstvOS)' == 'true' ">$(NoWarn);0649</NoWarn>
   </PropertyGroup>
   <PropertyGroup>
     <GeneratePlatformNotSupportedAssemblyMessage Condition="'$(TargetsAnyOS)' == 'true'">SR.Process_PlatformNotSupported</GeneratePlatformNotSupportedAssemblyMessage>
@@ -309,7 +309,7 @@
     <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.SchedGetSetAffinity.cs"
              Link="Common\Interop\Linux\Interop.SchedGetSetAffinity.cs" />
   </ItemGroup>
-  <ItemGroup Condition=" '$(TargetsOSX)' == 'true' or '$(TargetsiOS)' == 'true' or '$(TargetstvOS)' == 'true'">
+  <ItemGroup Condition=" '$(TargetsOSX)' == 'true'">
     <Compile Include="System\Diagnostics\Process.BSD.cs" />
     <Compile Include="System\Diagnostics\Process.OSX.cs" />
     <Compile Include="System\Diagnostics\ProcessManager.BSD.cs" />
@@ -345,7 +345,7 @@
     <Compile Include="$(CommonPath)Interop\FreeBSD\Interop.Process.GetProcInfo.cs"
              Link="Common\Interop\FreeBSD\Interop.Process.GetProcInfo.cs" />
   </ItemGroup>
-  <ItemGroup Condition="'$(TargetsUnknownUnix)' == 'true'">
+  <ItemGroup Condition="'$(TargetsUnknownUnix)' == 'true' or '$(TargetsiOS)' == 'true' or '$(TargetstvOS)' == 'true'">
     <Compile Include="System\Diagnostics\Process.UnknownUnix.cs" />
     <Compile Include="System\Diagnostics\ProcessManager.UnknownUnix.cs" />
     <Compile Include="System\Diagnostics\ProcessThread.UnknownUnix.cs" />

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

@@ -9,7 +9,7 @@ public partial class Process : IDisposable
         /// Creates an array of <see cref="Process"/> components that are associated with process resources on a
         /// remote computer. These process resources share the specified process name.
         /// </summary>
-        public static Process[] GetProcessesByName(string processName, string machineName)
+        public static Process[] GetProcessesByName(string? processName, string machineName)
         {
             throw new PlatformNotSupportedException();
         }
@@ -82,5 +82,6 @@ private string GetPathToOpenFile()
             throw new PlatformNotSupportedException();
         }
 
+        private int ParentProcessId => throw new PlatformNotSupportedException();
     }
 }