* Add new file mcl_flowers/bonemeal.lua, containing the bonemealing
callback for "mcl_core:dirt_with_grass".
* Override "mcl_core:dirt_with_grass" with a _mcl_on_bonemealing handler
calling a function defined in mcl_flowers. This sidesteps the problem
that bonemealing a node from mcl_core needs knowledge of mcl_flowers,
which would create a circular dependency. H/t to cora for suggesting
this solution. H/t to wsor for suggesting a solution that also works.
