refactor: Simplify trait generation for database encoding, decoding, and indexing

This commit refactors the encoding, decoding, and indexing traits in the sqlx-core library by introducing macros to generate the `AnyEncode`, `AnyDecode`, and `AnyColumnIndex` traits based on enabled features. This change enhances maintainability and reduces code duplication, while ensuring comprehensive support for various database combinations, including ODBC.

Author: lovasoa