CultureAndRegionInfoBuilder is not available in .NET core

For .NET 5 (and .NET Core), there is no [CultureAndRegionInfoBuilder](https://docs.microsoft.com/en-us/dotnet/api/system.globalization.cultureandregioninfobuilder?view=netframework-4.8&viewFallbackFrom=net-5.0) class.
For workaround, [this issue from dotnet/runtime](https://github.com/dotnet/runtime/issues/23802) may be relevant.

The documentation on [CultureInfo](https://docs.microsoft.com/en-us/dotnet/api/system.globalization.cultureinfo?view=net-5.0) still recommend developers to make use of CultureAndRegionInfoBuilder. This is concerned to be potentially misleading.