fix: improve object simulator.

[n1k0]

🔧 Problems

• The simulator doesn't show masses (total and per-item)
• The "add item" button is missing when the product items list is empty.
• When selecting an existing example or bookmark, we'd like to fill its name in the new bookmark text input.
• We'd also like a more meaningful query string representation than what we currently have.
• We want to render the steps impact distribution chart in the sidebar.

🍰 Solution

Implement or fix aforementioned tasks.

🏝️ How to test

• Check that the simulator renders total and per-item masses
• Check that we always have an "add item" button rendered.
• Check that an existing bookmark or example name is filled in the bookmark input text.
• Check that suggested bookmark names are more convenient than what we have now.
• Check that the step impacts distribution chart is rendered properly.

[n1k0]

@vjousse this is now ready for review.

[vjousse]

Some nits but code wise it looks good to me. Just a little question: why can't we add more than 2 processes? We may allow having twice the same process?

[n1k0]

Some nits but code wise it looks good to me. Just a little question: why can't we add more than 2 processes? We may allow having twice the same process?

@vjousse because we only have two processes available and having two distinct amounts of the same plastic would look weird I think… but that's probably some feedback we should get from POs.

[vjousse]

Shouldn't we display the density too to help understand the computation?

[n1k0]

I think it should be rendered in the explorer but here... I don't know, that would also clutter the ui. Let's wait for user feedback here.