dependLevel drove the order in which generateFinalScript() writes
objects, with higher levels emitted first so dependencies land before
whatever needs them, but nothing has assigned it since the React port
deleted schema_diff_dependency.js: every row got Object.keys' default
undefined bucket, so the script came out in whatever order the rows
happened to be in.
computeDependLevels() rebuilds the levels for the full result set from
each row's dependencies, walking the reverse graph so a row that other
rows depend on always ends up with the highest of their levels plus
one, with a cycle guard for the circular dependencies the script header
already warns about.
Fixes#10295.
f2fdef5ba5