Feature: #19494 - Add SELECTmmQuery method to DatabaseConnection

See Issue #19494

Description

A new method SELECT_mm_query has been added to the DatabaseConnection class. This method has been extracted from exec_SELECT_mm_query to separate the building and execution of M:M queries.

This enables the use of the query building in the database abstraction layer.

Example:

$query = SELECT_mm_query('*', 'table1', 'table1_table2_mm', 'table2', 'AND table1.uid = 1', '', 'table1.title DESC');