Speedup get_courses in lib/filebrowser/file_info_context_coursecat.php

During load testing on our very large instance, we noticed a slow query. This is caused by the query in get_courses in lib/filebrowser/file_info_context_coursecat.php. 

On the one hand, the query was called very frequently and also took a comparatively long time.

Environment:

• MySQL;
• course table: 400,000+ entries
• context table: 16.5+ million entries

Initial situation: Query runtime: 1,18s

The main problems are the "or" and a case- and accentsensitive search, which is not necessary.