Fix PendingModelChangesWarning for Unicode diacritics (NFC/NFD) on Linux

[TomasMoralesBarr]

Fixes #38191

Problem

On Linux/WSL2, string values containing diacritic characters (e.g. Café)
can be saved in NFD Unicode normalization form, while on Windows they are
typically NFC. EF Core's MigrationsModelDiffer used ordinal comparison
which treated NFC and NFD as different values, causing a false
PendingModelChangesWarning.

Fix

Normalize string values to NFC before comparison in DiffData().

Test

Added Seed_data_with_NFD_vs_NFC_unicode_string_is_considered_unchanged to
MigrationsModelDifferTest which confirms NFC and NFD strings representing
the same character produce no migration diff.

• I've read the guidelines for contributing and seen the walkthrough
• I've posted a comment on an issue with a detailed description of how I am planning to contribute and got approval from a member of the team
• The code builds and tests pass locally (also verified by our automated build checks)
• Commit messages follow this format:

        Summary of the changes
        - Detail 1
        - Detail 2

        Fixes #bugnumber

• Tests for the changes have been added (for bug fixes / features)
• Code follows the same patterns and style as existing code in this repo

[Copilot]

Pull request overview

Fixes false PendingModelChangesWarning on Linux/WSL2 caused by NFC vs NFD Unicode normalization differences when diffing seed data in migrations.

Changes:

• Normalize string seed-data values prior to comparison during MigrationsModelDiffer.DiffData().
• Add a regression test asserting that NFC and NFD equivalents in seed data produce no migration operations.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 5 comments.

File	Description
src/EFCore.Relational/Migrations/Internal/MigrationsModelDiffer.cs	Normalizes string values before comparing seed-data column modifications during diffing.
test/EFCore.Relational.Tests/Migrations/Internal/MigrationsModelDifferTest.cs	Adds a test covering NFC vs NFD equivalence for seed-data string values.

[Copilot]

Pull request overview

Addresses false PendingModelChangesWarning on Linux/WSL2 when seed data strings differ only by Unicode normalization form (NFC vs NFD), by normalizing string values prior to comparison in the seed data diff logic.

Changes:

• Normalize string seed values to NFC before equality comparison in MigrationsModelDiffer.DiffData().
• Add a regression test asserting that canonically equivalent NFC/NFD seed strings produce no migration operations.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 5 comments.

File	Description
src/EFCore.Relational/Migrations/Internal/MigrationsModelDiffer.cs	Normalizes string values (NFC) before comparing source/target seed data values.
test/EFCore.Relational.Tests/Migrations/Internal/MigrationsModelDifferTest.cs	Adds a regression test covering NFC vs NFD equivalence for seeded string values.

[AndriySvyryd]

I agree with @roji that a more robust way of fixing this is by using StringComparison.InvariantCulture in a new comparer returned from

efcore/src/EFCore/ChangeTracking/ValueComparer.cs

Line 258 in d86b520

public static ValueComparer CreateDefault(

That way it will also benefit the update pipeline.