Fix "Edit on eXeLearning and return to course" button.

[ignaciogros]

Fixes the Could not build platform integration URL from return URL error raised by eXeLearning
when sending the package back (Finish / File → Send to Moodle).

Same fix as mod_exescorm.

Cause

eXeLearning derives its Moodle callback endpoints (get_ode.php / set_ode.php) by splitting the
JWT returnurl on a known path, and only accepts /mod/exeweb, /mod/exescorm or
/course/section. The "return to course" button sends /course/view.php?id=N, which matches none
of them on Moodle 4.5.

Fix

Return targets outside the module are now wrapped in a new returnto.php, which lives under the
module path — so eXeLearning accepts it — and forwards the browser to the real destination.

• returnto.php (new): web entry point; validates the destination with PARAM_LOCALURL and
  redirects. Falls back to the activity's course.
• classes/exeonline/exeonline_redirector.php: wraps non-module return URLs (get_returnto_url())
  and resolves them back (resolve_returnto_url()).
• tests/exeonline/exeonline_redirector_test.php (new): 5 unit tests.

No database, language string or JavaScript changes.

Notes

• eXeLearning could also accept /course/view in buildIntegrationUrl(), but this fix works
  against already deployed instances.

Testing

Edit an eXeLearning Web activity → Edit on eXeLearning and return to course → Finish.
The package is saved and the browser lands on the course page.

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Moodle Playground Preview

The changes in this pull request can be previewed and tested using a Moodle Playground instance.

ℹ️ The eXeLearning editor is fetched from the shared release and unpacked into the plugin when the playground boots, so the first load may take a few extra seconds. ELPX upload, viewer and preview work normally.

[erseco]

The redirect flow and the additional tests look good to me. One minor suggestion: get_returnto_url() currently reimplements Moodle's local URL detection, and its HTTPS fallback is not exactly equivalent to moodle_url::out_as_local_url().

We could avoid exception-based control flow while still relying on Moodle's own semantics by checking $returnto->is_local_url() first and then calling out_as_local_url(false).

Not blocking from my side, since the current implementation only carries the local path and does not introduce an open redirect.

[ignaciogros]

Thanks for reviewing this.