implicit /+esm for JavaScript extensions

[mbostock]

EDIT: We reverted this in #1186 as it was breaking duckdb-wasm.

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This makes imports such as this work out of the box:

import Deck from "npm:deck.gl/dist.min.js";

import mermaid from "npm:mermaid/dist/mermaid.esm.min.mjs";

Previously these imports would error because they require /+esm; now the /+esm is added implicitly so it “just works.”

This also fixes the default entry for deck.gl, so that this now works, too:

import Deck from "npm:deck.gl";

(I did see an error once about “multiple versions of luma detected”… but couldn’t reproduce it reliably.)