Improve layout and drawing logic for STTextRenderView with clipsToContent support

- Refactor fragment layout height calculation in layout() to be more accurate and
  align with draw() behavior, using layoutFragmentFrame minY/maxY.
- Simplify drawing logic in draw() with a consistent fragment origin calculation.
- Adjust drawing offset when clipsToContent is enabled to ensure content is
  correctly aligned to y=0.
- Remove unnecessary originY accumulation and old comments that do not reflect
  the current implementation.