Support for npm:d3 and npm:htl

[Fil]

Salvage e651d6e and 72a4193 from the #458 PR: they allow a .ts or .js import to use d3 and htl with no linting or typescript errors. A test case (like an example) will be nice to have; see for example the examples/plot/ folder. Also check what happens with @observablehq/plot.

[Fil]

I don't know how to make this work; seems like the fix in 72a4193 was specific to dash being a part of client.

[mbostock]

This is a vague issue description (given that we obviously already support npm:d3 and npm:htl imports and it’s not clear what is specific to these libraries) and I’m now trying to remember what we‘re fixing here…

[mbostock]

I don’t see anything wrong here so closing as could not reproduce.