Implement support for "static" invoke imports in modules

[dglazkov]

Roughly, we want to be able to do this:

import gemini, { type GeminiInputs } from "@invoke/https://url/to/gemini.bgl.json";

Which will translate into:

1. Reading imports (fairly straightforward, since we have the whole TS runtime)
2. If there are imports starting with @invoke/, loading the https://url/to/gemini.bgl.json graph
3. If it's an imperative graph, getting its TS source
4. If that exists, supplying it to the TS VFS as if it's local so that GeminiInput resolves correctly. This would also ensure that gemini has the right shape.
5. Storing the graph in the dependencies array on the module

This would allow us to supply type information with graphs, which will be a huge productivity boost for imperative graph makers.

At runtime:

1. If there are any dependencies, load them
2. Add them as modules before starting QuickJS runtime.

[dglazkov]

Ah, maybe dependencies is a top-level GraphDescriptor property that allows storing all BGL dependencies as a flat list.