Should we recompute `AbstractGridIntegerConstant`s every time?

[pjaap]

After editing, e.g., the cell regions for a given grid, grid[NumCellRegions] is not updated. See:

julia> grid = simplexgrid(0:10);

julia> num_cellregions(grid)
1

julia> grid[CellRegions][4] = 2 # edit something
2

julia> num_cellregions(grid) # still = 1
1

julia> trim!(grid) # remove pre-computed data

julia> num_cellregions(grid) # now it is correct again
2

For me, especially functions like num_cellregions should compute the current number of cell regions and not return a cached value.
So I vote for recomputing AbstranctGridIntegerConstant in every get_index call. Also rename the type to AbstractGridInteger, since this is not a constant.

[j-fu]

I would agree with the renaming but I am not sure about the recomputation,
because in many cases this is an O(N) operation. If it would be named calculate_num_nodes I would agree...