Style ToastUI contextual menus

What does this MR do?

This MR style the ToastUI contextual menus to match our styling.

Screenshots

Does this MR meet the acceptance criteria?

TODO

• Style contextual menus
• Implement GlTooltipDirective to ensure tooltips are displayed correctly
• Add/update tests
• UX review
• Code review

Conformity

• Changelog entry
• Code review guidelines
• Merge request performance guidelines
• Style guides

Issue #216797 (closed)