libghostty: expose row cell styling bit

Add a render row-cells data key for querying whether the current cell has
explicit styling. This lets consumers avoid fetching a raw cell or full style
snapshot when all they need is the cell's HasStyling bit.

The new key is appended to the existing enum for ABI safety and is served by
the existing row-cells getter path. Existing data keys and function exports are
unchanged.

include/ghostty/vt/render.h

@@ -607,6 +607,13 @@ typedef enum GHOSTTY_ENUM_TYPED {
    *  GHOSTTY_RENDER_STATE_ROW_DATA_SELECTION once per row and applying that
    *  range directly, avoiding one C API call per cell for selection state. */
   GHOSTTY_RENDER_STATE_ROW_CELLS_DATA_SELECTED = 7,
+
+  /** Whether the cell has any explicit styling (bool).
+   *  This is equivalent to querying the raw cell's
+   *  GHOSTTY_CELL_DATA_HAS_STYLING value, but avoids materializing the raw
+   *  GhosttyCell for renderers that only need to know whether fetching the
+   *  full style is necessary. */
+  GHOSTTY_RENDER_STATE_ROW_CELLS_DATA_HAS_STYLING = 8,
   GHOSTTY_RENDER_STATE_ROW_CELLS_DATA_MAX_VALUE = GHOSTTY_ENUM_MAX_VALUE,
 } GhosttyRenderStateRowCellsData;