Enhance transparency handling across UI components
- Updated multiple UI classes to utilize the new `getCurrentTransparency()` method for consistent transparency management, improving visual coherence across the application.
- Adjusted drawing methods in various controls, including `LLAccordionCtrlTab`, `LLButton`, `LLContainerView`, and others, to apply transparency correctly to colors and images.
- Introduced caching mechanisms for transparency values in `LLUICtrl`, optimizing performance during rendering.
- Ensured that transparency settings are correctly propagated through parent-child relationships in the UI hierarchy, enhancing overall user experience.
