func ComputeEdits(before, after string) []diff.Edit
ComputeEdits returns the diffs of two strings using a simple line-based implementation, like diff.Strings.
Deprecated: this implementation is moribund. However, when diffs appear in marker test expectations, they are the particular diffs produced by this implementation. The marker test framework asserts diff(orig, got)==wantDiff, but ideally it would compute got==apply(orig, wantDiff) so that the notation of the diff is immaterial.