ggml : better way to express implicit node dependencies in a graph

[Georgi Gerganov]

Operations on views can introduce implicit dependencies between the nodes in the compute graph which often lead to bugs when we forget about these dependencies.

See ggerganov/llama.cpp#3012 for more context

We need to find some better way to handle such cases.
One option is to introduce ggml_depends_on() which if not ideal, should at least make the code more explicit less error prone.