Issue #3592010: Add index Views data key helper
This adds IndexInterface::getViewsDataKey() so code can ask the search index for its Views data key instead of repeating the search_api_index_ prefix manually.
The Views hook implementation now uses the new method when building base table keys and plugin base lists. I also added a small kernel assertion for the generated key.
Checked locally:
- composer validate --no-check-publish
- php -l on changed PHP files
- git diff --check
I also tried composer install, but this module-only checkout does not have the Drupal package repository configured for the dev dependencies.
Closes #3592010