Feat: improve the interactivity of the b_plus_tree_printer

[I-can-do-fourier]

This PR(for macos)aims at improving the interactivity of the b_plus_tree_printer running on our local machine. At present, every time we want to show our result of a bpt, we need to use the command g my-tree.dot, then type dot -Tpng -O my-tree.dot in another terminal. Finally, we should open/refresh the PNG image to show the results. It wastes a lot of time if we want to examine our implementation step by step.

This PR adds a new command 's' in the b_plus_tree_printer.cpp. After typing 's', the tree will be stored and converted to the png file. Then the tree image will be open/refresh on the screen. We can split the image to the right side of the screen and print step by step.

[skyzh]

Thanks for the PR but I feel it would be better if students can compile their implementation to WASM so that they can visualize in the browser (as in wasm_bpt_printer)?

[I-can-do-fourier]

Thanks for the PR but I feel it would be better if students can compile their implementation to WASM so that they can visualize in the browser (as in wasm_bpt_printer)?

Thank you, skyzh. I didn't notice there is already a wasm_bpt_printer in our source code. Could you please give me some instructions on how to use this? I try to use make wasm-bpt-printer -j$(nproc) but it fails. I am not very familiar with c++ and cmake.