Support import assertions on import declarations in the REPL

[dsherret]

Just need to transform it correctly:

> import data from "./test.json" assert { type: "json" };
Uncaught TypeError: Expected a "JavaScript" module but loaded a "JSON" module.
    at async <anonymous>:2:28

Also, maybe ensure that for export declarations it just doesn't error.

Workaround:

const data = (await import("./test.json", { assert: { type: "json" } })).default;