Update globalization-icu.md to detail differences in string equality and sorting

[daverayment]

Summary

(Part of a documentation fix for CompareOptions API issue #41052 )

An update to detail the differences between NLS and ICU implementations for string equality and sorting:

• Ligatures are not regarded as equal to their expanded forms under ICU by default (CompareOptions.IgnoreNonSpace must be used to override this). This is because of the different collation strength between NLS and ICU.
• The default sort order for strings has changed under ICU, effectively removing the previous None functionality and making StringSort the default. The only way to restore previous None ordering is to switch back to NLS.

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Internal previews

📄 File	🔗 Preview link
docs/core/extensions/globalization-icu.md	.NET globalization and ICU