Support new Moodle directory structure

[kabalin]

Evaluate implications of Moodle code directories restructure MDL-83424 on moodle-plugin-ci. Moving code into /public directory is likely to affect installation and testing.

Fix needs to adjust location-related behaviour for Moodle versions 5.0 and below.

In order to test before MDL-83424 is integrated, use https://github.com/andrewnicols/moodle/tree/MDL-83424-main

(quick test using Andrew's repo: https://github.com/kabalin/moodle-plugin-ci/actions/runs/15325216030/job/43118021606 )