Add INSTR as alias of positionCaseInsensitive for MySQL compatibility

Why it matters

Enables users migrating from MySQL or working in mixed environments to use the familiar INSTR function for case-insensitive substring searches, improving query compatibility and easing transition.

How to use it

Use the INSTR function in your SQL queries as a case-insensitive substring search, similar to positionCaseInsensitive. For example:

SELECT INSTR('Hello World', 'world');

This will return the position of the substring ignoring case.