Fix locale (icudt.dat) related stuff when targeting iOS

[lemonmojo]

Some unit tests succeed when targeting macOS but fail when targeting the iOS simulator.
They are marked with // TODO: Test fails on iOS.

[lemonmojo]

Just verified on an actual iPhone; fails as well.

[lemonmojo]

Here's a list of all the APIs I've found to SIGSEGV up until now:

System.Type.GetType
System.String.IndexOf
System.DateTime.Now
System.Globalization.CultureInfo ctor
System.Version ctor
System.Version.TryParse
System.Convert.ToInt32
System.Reflection.Assembly.GetName
System.Decimal.TryParse

[lemonmojo]

Setting InvariantGlobalization in the csproj to true works around the crashes but makes tests using a specific culture fail.

[lemonmojo]

Can also be fixed by having <RuntimeHostConfigurationOption Include="ICU_DAT_FILE_PATH" Value="icudt.dat" /> in the csproj and including a copy of icudt.dat in the bundle.
The file can be found in the NuGet cache (ie. ~/.nuget/packages/microsoft.netcore.app.runtime.nativeaot.ios-arm64/8.0.0-preview.6.23329.7/runtimes/ios-arm64/native/icudt.dat)

[lemonmojo]

Unfortunately that doesn't work in a XCTest bundle because the runtime locates the file by using -[NSBundle mainBundle].
See dotnet/runtime#88835 and xamarin/xamarin-macios#18471 (comment)

[lemonmojo]

Might be able to work around this by calling AppContext.SetData("ICU_DAT_FILE_PATH", "<path>") early on in startup.

[lemonmojo]

Using System.AppContext to set the icudt.dat file path at runtime does indeed work.
See f2d4f2b.