Issue #3515192: Add asterisk to overridden sections in Views UI

Added asterisk () indicators to Views UI section headers when they are overridden from the default display. This provides immediate visual feedback to help users identify which sections like Fields, Relationships*, and Filters* have been customized in each display. Implemented via preprocessing function in views_ui.theme.inc rather than template modifications to ensure compatibility with all admin themes (Claro, Gin, Seven, custom themes). The asterisk is appended to the section title when #overridden is TRUE, leveraging existing Drupal override detection logic.

Screencast_from_2025-08-01_10-45-44

Closes #3515192