More stern warning about string culture comparison

[Smaug123]

Summary

Add a further warning about InvariantCulture in string comparison methods.

It continues to be true that you need to read lots of documentation before using String.StartsWith and friends, and the docs continue not to tell you that this is the case. This PR elevates some more of the most critical information from Best Practices for Using Strings to the API docs.

Source for "rarely appropriate" is Best Practices:

On balance, the invariant culture has few properties that make it useful for comparison. It does comparison in a linguistically relevant manner, which prevents it from guaranteeing full symbolic equivalence, but it isn't the choice for display in any culture. One of the few reasons to use StringComparison.InvariantCulture for comparison is to persist ordered data for a cross-culturally identical display. For example, if a large data file that contains a list of sorted identifiers for display accompanies an application, adding to this list would require an insertion with invariant-style sorting.

ref: #8973

[learn-build-service-prod]

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[MSDN-WhiteKnight]

I don't think this change is needed. These notes basically say "This overload uses current culture implicitly, but this might be unexpected. Consider instead using overload that explicitly accepts culture." Nowhere it was implied that InvariantCulture should be used. It is not useful to add that InvariantCulture is rarely appropriate, it's too vague, and too disconnected from the preceding text. If any addition is needed here, it should be more actionable, something like "If you don't need linguistic comparison, consider using StringComparison.Ordinal instead".

[tarekgh]

@Smaug123 thanks for submitting the PR and updating the note. The new suggested changes LGTM.

[learn-build-service-prod]

Learn Build status updates of commit 046e927:

✅ Validation status: passed

File	Status	Preview URL	Details
xml/System/String.xml	✅Succeeded	View

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[learn-build-service-prod]

Learn Build status updates of commit b3a3dbd:

✅ Validation status: passed

File	Status	Preview URL	Details
xml/System/String.xml	✅Succeeded	View

For more details, please refer to the build report.

For any questions, please:

• Try searching the learn.microsoft.com contributor guides
• Post your question in the Learn support channel