feat: index column ordering in migrations

[olavloite]

Support index column ordering in migrations.

Credits: @sdahps

Replaces #631
Fixes #630

[gemini-code-assist]

Summary of Changes

Hello @olavloite, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request enhances the migration capabilities by allowing developers to define the ordering (ascending or descending) of columns within an index. This provides greater control over index creation, ensuring that the generated SQL accurately reflects the desired index structure for performance optimization and data retrieval patterns. The change involves updating the SQL generation logic and adding corresponding model and test definitions.

Highlights

• Index Column Ordering: Introduced support for specifying ascending or descending order for columns within an index definition during migrations.
• Migration SQL Generation: Modified the SpannerMigrationsSqlGenerator to correctly generate SQL for indexes that include column ordering.
• Test Coverage: Added new test cases to verify that indexes with mixed ascending and descending column orders are generated correctly in migration scripts.

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[gemini-code-assist]

Code Review

This pull request adds support for specifying column sort order in indexes during migrations, which is a valuable feature. The approach of using the standard EF Core IsDescending() API is correct. The changes include corresponding test updates, which is great. However, there's a critical issue in SpannerMigrationsSqlGenerator.cs where a new method GenerateIndexColumnList is called but its definition is missing from the provided files. This will prevent the code from compiling. I've left a specific comment with a suggested implementation to resolve this.

[bhatt4982]

LGTM...

[bhatt4982]

LGTM