Feature request: add debug toolbox `ggml-debug.h`

[ngxson]

Having hacked around ggml-easy for a while, I was thinking about idea of having a debugging toolbox inside ggml itself. Such toolbox can be an useful tool for users who haven't yet familiar with inner work of ggml.

For now, I'm thinking about these tools:

• ggml_set_debug(struct ggml_tensor * t) which prints the tensor as soon as it is calculated. An use case is described here: helper function to examine tensor data for any backend? #1155 (comment)
• ggml_graph_dump_dot and ggml_graph_print: we already have this, but can count as a debugging tool
• ggml_backend_sched_print_buffers: print allocated buffer size for each backend
• Probably a tool to debug graph splits like the one introduced in add ggml_backend_sched_dump_dot llama.cpp#10825

For the implementation, I'm thinking about grouping these tool into a ggml-debug.h header. It should not be included in production-ready code.

However, I don't yet have an idea for detail implementation. Would love to discuss more on this.