Improve Process support on MacCatalyst

[adamsitnik]

1. Performance: prefer posix_spawn when available (it has provide up to x100 boost on macOS arm64). It's a matter of extending what Prefer posix_spawn on OSX #126063 did by adding || defined(TARGET_MACCATALYST) here:

- #if defined(TARGET_OSX)
+ #if defined(TARGET_OSX) || defined(TARGET_MACCATALYST)

2. Perform IsTerminal check for MacCatalyst:

We never performed the extra configuration on these platforms:

For IsiOSLike platforms:

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

Line 14 in 1d46816

<IsiOSLike Condition="'$(TargetPlatformIdentifier)' == 'maccatalyst' or '$(TargetPlatformIdentifier)' == 'ios' or '$(TargetPlatformIdentifier)' == 'tvos'">true</IsiOSLike>

We were including:

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

Lines 298 to 300 in 1d46816

	<ItemGroup Condition="'$(TargetPlatformIdentifier)' != '' and '$(TargetPlatformIdentifier)' != 'windows' and '$(IsiOSLike)' == 'true'">
	<Compile Include="System\Diagnostics\Process.ConfigureTerminalForChildProcesses.iOS.cs" />
	</ItemGroup>

That was a nop:

runtime/src/libraries/System.Diagnostics.Process/src/System/Diagnostics/Process.ConfigureTerminalForChildProcesses.iOS.cs

Lines 6 to 20 in 1d46816

	public partial class Process
	{
	/// These methods are used on other Unix systems to track how many children use the terminal,
	/// and update the terminal configuration when necessary.
	[Conditional("unnecessary")]
	internal static void ConfigureTerminalForChildProcesses(int increment, bool configureConsole = true)
	{
	}
	static partial void SetDelayedSigChildConsoleConfigurationHandler();
	private static bool AreChildrenUsingTerminal => false;
	}
	}

The fix will be to stop treating MacCatalyst as iOSLike in the project file:

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

Line 14 in ab81350

<IsiOSLike Condition="'$(TargetPlatformIdentifier)' == 'maccatalyst' or '$(TargetPlatformIdentifier)' == 'ios' or '$(TargetPlatformIdentifier)' == 'tvos'">true</IsiOSLike>

and extend pal_log.m (context) with sth like:

int32_t SystemNative_IsATty(intptr_t fd)
{
#if defined(TARGET_MACCATALYST)
    return isatty(ToFileDescriptor(fd));
#elif defined(TARGET_IOS) || defined(TARGET_TVOS)
    // there is no terminal on these platforms
    (void)fd;
    return 0;
#endif
}

We need to get #126306 merged first and ensure all the MacCatalyst and iOS builds and tests are green.

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[adamsitnik]

cc @rolfbjarne

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