Update headings font selector: drop tp-caption, add Bootstrap 5 classes

[jjroelofs]

Linked issues

• Update headings font selector: drop tp-caption, add Bootstrap 5 classes #798

Solution

Updated the default headings_font_face_selector to remove the obsolete Revolution Slider .html .tp-caption selector and add Bootstrap 5 heading classes (.h1–.h6, .display-1–.display-6).

Checklist

• I have read the CONTRIBUTING.md document.
• My commit messages follow the contributing standards and style of this project.
• My code follows the coding standards and style of this project.
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Need to run update.php after code changes
• Requires a change to end-user documentation.
• Requires a change to developer documentation.
• Requires a change to QA tests.
• Requires a new QA test.
• I have updated the documentation accordingly.
• All new and existing tests passed.