Add Back indexHint Function to Fix Issues #21238 and #9540

Why it matters

The indexHint function helps optimize query execution by guiding the query planner to use specific indexes. This feature addresses issues reported in #9540 and #21238, restoring a valuable ability that was removed in a previous change (#9542). By using indexHint, users can improve performance for certain query patterns where explicit index control is beneficial.

How to use it

Use the indexHint function within your SQL queries to specify which index should be used by the query engine. For example:

SELECT * FROM table WHERE indexHint('index_name') AND condition

This hints the query planner to prioritize the named index for query optimization.