A pure function of its props: the layer calls it directly inside its cached tiles, not as a
component, so it can hold no state and call no hook (a hook throws). It returns the cell's root,
which applies props.style to place itself in the cell; CellContent is that root ready-made.
The layer takes no pointer events; the part that should take the pointer spreads
props.interactiveProps.
Draws a cell's content in place of its text.