#[dispatch]Expand description
Generate walk, map, visit, or mutate dispatch from an inherent impl.
#[dispatch(visit, policy = expr)] and #[dispatch(mutate, policy = expr)]
use a ContextPolicy<Self> or MutContextPolicy<Self> for default recursion.
The expression runs at each default descent and may read self for configuration;
mutable traversal state stays on self. Policy tuples compose as usual.