[rc2] Ignore line endings when comparing strings in MigrationsModelDiffer

[AndriySvyryd]

Fixes #35382

Description
In EF9 we added a warning when applying migrations and the current model doesn't match the model snapshot from the latest migration. However, the migrations might be generated on a machine with a different OS than the machine that compiles the app. This results in a false positive warning if the model contains any multi-line strings.

Customer impact
If the user has configured warnings to throw by default, then this will result in an exception (usually on startup) in the above scenario. The workaround is to suppress this warning.

How found
This was reported by multiple users on EF9

Regression
Yes, from EF8

Testing
Tests added.

Risk
Low, only affects model diffing logic

[Copilot]

Pull Request Overview

This PR fixes a cross-platform compatibility issue where EF9's migration model diffing incorrectly detected changes due to line ending differences between operating systems. The fix ensures that multi-line strings in models are compared while normalizing line endings.

Key changes:

• Introduces a MultilineEquals helper method that normalizes line endings before string comparison
• Updates all string comparisons in the MigrationsModelDiffer to use this normalized comparison for SQL and comment fields
• Adds comprehensive test coverage for various scenarios involving line ending differences

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/EFCore.Relational/Migrations/Internal/MigrationsModelDiffer.cs	Adds MultilineEquals helper and updates string comparisons to normalize line endings
test/EFCore.Relational.Tests/Migrations/Internal/MigrationsModelDifferTest.cs	Adds comprehensive test cases covering line ending normalization scenarios
test/EFCore.Specification.Tests/TestUtilities/ListLoggerFactory.cs	Simplifies line ending normalization using ReplaceLineEndings()

[artl93]

Rc2 previous regression