[installer] extra copy of libMonoPosixHelper.dylib for libZipSharp.dll

[jonathanpeppers]

Context: https://github.com/jonathanpeppers/foo/blob/Microsoft.NET.Sdk/foo.csproj

I've been experimenting with trying to multi-target "legacy"
Xamarin.Android and .NET 6 with:

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <TargetFrameworks>monoandroid11.0;net6.0-android</TargetFrameworks>
  </PropertyGroup>
</Project>

I got this to work fairly well on Windows with some hacks, but it
completely fails on macOS:

error XACML7000: System.DllNotFoundException: Unable to load shared library 'MonoPosixHelper' or one of its dependencies. In order to help diagnose loading problems, consider setting the DYLD_PRINT_LIBRARIES environment variable: dlopen(libMonoPosixHelper, 1): image not found
error XACML7000:    at Mono.Unix.Native.Syscall.lstat(String file_name, Stat& buf)
error XACML7000:    at Xamarin.Tools.Zip.Utilities.StatFile(String path, Boolean followSymlinks, Stat& sbuf) in /Users/runner/work/1/s/Utilities.Unix.cs:line 58
error XACML7000:    at Xamarin.Tools.Zip.Utilities.GetFileType(String path, Boolean followSymlinks, FilePermissions& fileType) in /Users/runner/work/1/s/Utilities.Unix.cs:line 147
error XACML7000:    at Xamarin.Tools.Zip.UnixPlatformServices.IsFileOfType(String path, FilePermissions mode, Boolean& result) in /Users/runner/work/1/s/UnixPlatformServices.cs:line 428
error XACML7000:    at Xamarin.Tools.Zip.UnixPlatformServices.IsDirectory(ZipArchive archive, String path, Boolean& result) in /Users/runner/work/1/s/UnixPlatformServices.cs:line 40
error XACML7000:    at Xamarin.Tools.Zip.PlatformServices.<>c__DisplayClass9_0.<IsDirectory>b__0(IPlatformServices services) in /Users/runner/work/1/s/PlatformServices.cs:line 73
error XACML7000:    at Xamarin.Tools.Zip.PlatformServices.CallServices(Func`2 code) in /Users/runner/work/1/s/PlatformServices.cs:line 165
error XACML7000:    at Xamarin.Tools.Zip.PlatformServices.IsDirectory(ZipArchive archive, String path) in /Users/runner/work/1/s/PlatformServices.cs:line 73
error XACML7000:    at Xamarin.Tools.Zip.ZipArchive.AddFile(String sourcePath, String archivePath, EntryPermissions permissions, CompressionMethod compressionMethod, Boolean overwriteExisting) in /Users/runner/work/1/s/ZipArchive.cs:line 397
error XACML7000:    at Xamarin.Android.Tasks.ZipArchiveEx.AddFiles(String folder, String folderInArchive, CompressionMethod method)
error XACML7000:    at Xamarin.Android.Tasks.ZipArchiveEx.AddDirectory(String folder, String folderInArchive, CompressionMethod method)
error XACML7000:    at Xamarin.Android.Tasks.CreateManagedLibraryResourceArchive.<>c__DisplayClass39_0.<RunTask>b__0(String f)
error XACML7000:    at Xamarin.Android.Tools.Files.ArchiveZipUpdate(String target, Action`1 archiver)
error XACML7000:    at Xamarin.Android.Tasks.CreateManagedLibraryResourceArchive.RunTask()
error XACML7000:    at Xamarin.Android.Tasks.AndroidTask.Execute()

Comparing a regular .NET 6 build, it works because
libMonoPosixHelper.dylib is sitting right next to libZipSharp.dll.

Comparing a regular "legacy" Xamarin.Android build, it works because
libMonoPosixHelper.dylib is loaded via:

Mono: DllImport loaded library '/Library/Frameworks/Mono.framework/Versions/6.12.0/lib/../lib/libMonoPosixHelper.dylib'

We're lucky this works, as it is using a Mono system
libMonoPosixHelper.dylib instead of the one from Xamarin.Android.

I could solve the problem locally by running:

cd /Library/Frameworks/Xamarin.Android.framework/Versions/Current/lib/xbuild/Xamarin/Android/lib/host-Darwin/
sudo cp libMonoPosixHelper.dylib ../../

I updated our installer to include the copy of
libMonoPosixHelper.dylib that libZipSharp.dll expects.