Refactor constraint deletions and GRBupdatemodel

[odow]

The MOI wrapper eagerly updates the row indices of constraints in a model upon deletion:

Gurobi.jl/src/MOI_wrapper/MOI_wrapper.jl

Lines 2115 to 2129 in 38464c2

	ret = GRBdelconstrs(model, length(rows_to_delete), rows_to_delete)
	_require_update(model)
	for (_, info) in model.affine_constraint_info
	# The trick here is: searchsortedlast returns, in O(log n), the
	# last index with a row smaller than info.row, over rows_to_delete
	# this is the same as the number of rows deleted before it, and
	# how much its value need to be shifted.
	info.row -= searchsortedlast(rows_to_delete, info.row - 1)
	end
	cs_values = sort!(getfield.(cs, :value))
	# If the key of an model.affine_constraint_info entry is in cs_values,
	# then that entry is deleted.
	filter!(model.affine_constraint_info) do pair
	return isempty(searchsorted(cs_values, pair.first))
	end

We should instead do what we do for variables and lazily delay the update until the next call to GRBupdatemodel:

Gurobi.jl/src/MOI_wrapper/MOI_wrapper.jl

Lines 981 to 986 in 38464c2

	ret = GRBdelvars(model, length(del_cols), del_cols)
	_check_ret(model, ret)
	for var_idx in indices
	delete!(model.variable_info, var_idx)
	end
	append!(model.columns_deleted_since_last_update, del_cols .+ 1)

Gurobi.jl/src/MOI_wrapper/MOI_wrapper.jl

Lines 520 to 534 in 38464c2

	sort!(model.columns_deleted_since_last_update)
	for var_info in values(model.variable_info)
	# The trick here is: searchsortedlast returns, in O(log n), the
	# last index with a column smaller than var_info.column, over
	# columns_deleted_since_last_update this is the same as the number
	# of columns deleted before it, and how much its value need to be
	# shifted.
	var_info.column -= searchsortedlast(
	model.columns_deleted_since_last_update,
	var_info.column,
	)
	end
	model.next_column -= length(model.columns_deleted_since_last_update)
	empty!(model.columns_deleted_since_last_update)
	ret = GRBupdatemodel(model)

This also explains why we didn't trigger #515 for variable deletion: #515 (comment)

[odow]

Closed by #552