Determine Turkish casing from the locale name instead of collation

[MsfPablo]

Fixes #106560

Problem

On Android, "i".ToUpper(new CultureInfo("tr-TR")) returns I (U+0049) instead of İ (U+0130), and "I".ToLower(...) returns i instead of ı. The same code is correct on Windows/Linux/macOS.

Cause

TextInfo.NeedsTurkishCasing does not look at the locale at all — it infers the need for Turkish casing by probing the collation tailoring:

return CultureInfo.GetCultureInfo(localeName).CompareInfo.Compare("ı", "I", CompareOptions.IgnoreCase) == 0;

Android uses the system ICU, which does not carry the tr/az collation tailoring that makes U+0131 compare equal to I under IgnoreCase (the same underlying gap tracked by #60568). The probe therefore returns false for tr-TR, IcuChangeCase takes the ChangeCase path instead of ChangeCaseTurkish, and the dotted/dotless i mapping is silently lost. GlobalizationNative_ChangeCaseTurkish itself is fine and is already built for Android — it is simply never called.

Fix

Decide from the locale's language subtag instead, which is what ICU itself does (ustrcase_getCaseLocale selects UCASE_LOC_TURKISH for languages tr and az). This removes the dependency on collation data and makes the behavior identical on every ICU platform.

This should be behavior-preserving elsewhere: tr and az are exactly the languages whose collation tailoring made the old probe return true, and the root collation does not equate U+0131 with I. The existing en-US-POSIX regression case — which exists precisely because the old check was collation-based — still passes, since its language subtag is en.

Tests

The Turkish ToUpper/ToLower cases in TextInfoTests were skipped on Android/LinuxBionic with the comment "Android has its own ICU, which doesn't work well with tr". Those guards are removed so the cases now run on those platforms and cover this fix. They exercise tr, tr-TR, az and az-Latn-AZ.

Verification

I want to be upfront: I have not built or run this locally. Building dotnet/runtime for Android and running the globalization suite on a device/emulator was not something I could do in my environment, so I am relying on CI (including the Android legs) to validate it. The change is small and self-contained, and the re-enabled test cases are the intended proof. Happy to iterate if CI shows anything unexpected — in particular if some locale I have not considered relied on the old collation-derived answer.

cc @matouskozak @tarekgh @ilonatommy

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