Core compatibility with ILIAS: Add helpers for platform-specific paths and input rendering

[Saaweel]

Hi all,

As part of the ongoing STACKForILIAS 11.0.0 work, this PR adds a few small extension points to STACK core that allow ILIAS to reuse the same code without carrying local copies of Moodle-specific paths and rendering details.

The changes are intentionally minimal and preserve existing Moodle behaviour:

• Add stack_plot_url_base() and stack_cors_scripts_dir() in locallib.php.
• Use these helpers when rendering question-library plots and checking JSXGraph/Parsons styles.
• Extend replace_validation_tags() with an optional custom validation value.
• Add get_name() to the base input API.
• Keep equivalence validation markup unchanged in Moodle, while using valid block markup outside Moodle.
• Purge cached CAS results when their STACK-Maxima version is incompatible.

These changes are needed by STACKForILIAS, but are neutral for Moodle and reduce future divergence between both integrations.

Validated with PHP lint and on Moodle 5.2 using the STACK healthcheck, including CAS, cache, plots, JSXGraph and Parsons.

Kind regards,
Saúl
SURLABS

[sangwinc]

Thanks @Saaweel that's really very helpful. We'll review these (when the holidays are over) and sort out some mechanism to implement the changes you need. Please let us know of anything similar.