Unify styling of info boxes

[ml-evs]

There's now three sources of "info" about blocks:

1. hovering over the entry in the add a block menu
2. hovering over the (i) button in the block title
3. hovering over certain fields in the block
4. hovering over field names in the edit page (introduced in Test out self-hosted runner for e2e tests #1410)

They should probably all use the same component, but atm they do not. Some differences I'm aware of:

• (1) obeys line breaks but (2) does not (see e.g., echem block)
• (3) uses native html alt text so is not styled at all

[ml-evs]

Related: we should show block version numbers in the info box for blocks, now that block version != datalab version