Add visibility control to support Jupyter meta tags

[GYHHAHA]

This is a initial version for the implementation. More comments/discussion/suggestion needed to do a better refinement. See #50 and executablebooks/mystmd#407.

[GYHHAHA]

@rowanc1 Sorry about the long-time pause here! I'm still kind of busy recently. Feel free to close if you are going to implement with approach from your side, and I wish this pr should not be a blocker or something similar. Otherwise, just leave it open, so I may take a try sometime in the future.

[drewlio]

Is this feature still planned? It seems like I can hide remove input from native jupyter code cells in myst-nb but not in mystmd. Also in jupyer book.

[rowanc1]

It is still planned, we will likely revive this branch soon. You can currently remove, but not hide cells/outputs/inputs.

[drewlio]

@rowanc1 Thanks.

I'm learning this whole myst ecosystem and working to understand what features are ready. I'm focused on creating PDF output, btw.

Could I ask the following questions, please?

1. Lack of this feature in myst-theme doesn't effect PDF output, correct?
2. 🏷 Propagate block metatags to code node and output node mystmd#407 implemented this in mystmd and was merged as v1.0.2. This PR is what should make it work via the cli for PDF output, correct?

If the answer to both is yes, then maybe I need to open an issue because even remove-input isn't working.