Document new SQL Server vector and full-text search features

[roji]

See dotnet/efcore#37536
See dotnet/efcore#37538
See dotnet/efcore#37578

[AndriySvyryd]

Add full-text-search.md to ToC

[Copilot]

Pull request overview

Adds EF Core 11 documentation covering new SQL Server capabilities around approximate vector search (VECTOR_SEARCH + vector indexes) and full-text search table-valued functions, along with supporting provider docs and cross-links.

Changes:

• Document SQL Server VECTOR_SEARCH()/vector indexes and full-text search TVFs in EF Core 11 “What’s New”.
• Expand SQL Server vector search provider docs with approximate search, vector indexes, and a hybrid search example.
• Add a new SQL Server full-text search provider documentation page and link it from the SQL Server functions mapping page.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 10 comments.

File	Description
entity-framework/core/what-is-new/ef-core-11.0/whatsnew.md	Adds EF Core 11 release notes content for SQL Server vector search and full-text search TVFs.
entity-framework/core/providers/sql-server/vector-search.md	Extends vector search docs to include approximate search/indexing and hybrid search guidance.
entity-framework/core/providers/sql-server/functions.md	Adds a “See also” cross-link to the new SQL Server full-text search documentation page.
entity-framework/core/providers/sql-server/full-text-search.md	Introduces a new SQL Server full-text search documentation page (predicates + TVFs).