Improve invariant globalization mode to be more complete

[marek-safar]

The improvements to make invariant globalization mode more complete have been suggested since this mode was introduced. This issue extracts information from various existing comments and suggestion for easier .NET6 tracking.

• Make basic lower/upper casing of non-ASCII characters work. The experience is pretty bad today if you are non-English speaking and like to use your native alphabet. The size footprint for doing this does not seem prohibitive.
• Throw exceptions when somebody asks for non-invariant culture-specific data to make the bugs caused by missing globalization support easy to discover. We return bogus invariant data silently today.

Related issues

• Breaking change proposal: OrdinalIgnoreCase string comparison, ToUpperInvariant, and ToLowerInvariant to use ICU on all platforms #30960
• Proposal: Enable globalization invariant mode for all runtime images dotnet-docker#1877
• https://github.com/dotnet/designs/blob/main/accepted/2020/mono-convergence/globalization-support-in-.net5.md#enhanced-invariant-mode

Tagging subscribers to this area: @tarekgh, @safern, @krwq
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[GrabYourPitchforks]

Also related: #20674, which is philosophically a "how do we want OrdinalIgnoreCase to behave in an ICU world?" question.

[Wraith2]

Libraries can require globalization information to function correctly, for example SqlClient. Currently the way to check if the library is running in invariant mode is CultureInfo.GetCultureInfo("en-US").EnglishName.Contains("Invariant") which could be slow if it causes a culture instantiation and isn't obvious. It would be nice if there were a cleaner way to detect the mode.

[tarekgh]

Throw exceptions when somebody asks for non-invariant culture-specific data to make the bugs caused by missing globalization support easy to discover. We return bogus invariant data silently today.

I would be careful doing that. apps using libraries which they don't control and libraries can be creating non invariant cultures. Apps will not have any choice at that time but not using such libraries.

[jkotas]

We can add compat quirks if we find this to be a problem.

[tarekgh]

We can add compat quirks if we find this to be a problem.

I am pretty sure we'll get a lot of noises with that and the volume of complain can be none trivial.