Document UseSqlReturningClause and UseSqlOutputClause

[roji]

For issue dotnet/efcore#29916.

We should:

• Update the SQL Server page documenting the trigger workaround
• Update the EF 7.0 breaking change note to point users to using the new APIs if on 8.0
• Add docs on UseSqlReturningClause in the SQLite provider section

[SeeIfIDont]

There appears to be a link reserved for this purpose when the old SQL generator was obsoleted.