Issue #3607798: Warn when return-to-workflow is set with an inline or modal confirmation type

Adds a guardrail for the webform resume handler's "Return to the workflow after submit" option (return_to_workflow, added in #3607206).

The redirect back to the interaction dispatcher is issued from the handler's confirmForm(), which webform runs after setConfirmation(). The inline and modal confirmation types call $form_state->setRebuild() and re-render the form in place, which cancels that redirect, so chaining silently does nothing. This is easy to misconfigure (it bit a downstream consumer).

Change

• OrchestraResumeHandler::buildConfigurationForm() now shows a warning webform_message on the option when the form's confirmation type is inline or modal, visible via #states while the option is on, telling the author to use a redirecting type (for example Page).
• Documents the constraint in docs/interaction.md.
• WebformTaskReviewTest::testInlineConfirmationWarning() asserts the warning shows for an inline confirmation and is gone for a redirecting one.

Verification

Full WebformTaskReviewTest green locally (7 tests, 63 assertions); phpcs (Drupal) and php -l clean on the changed files.