[@web/test-runner] How do we disable all source transforms?

[trusktr]

Web Test Runner out of the box is modifying my import statements, which leads to this issue:

• [@web/test-runner] Very basic Solid.js example not working inside Web Test Runner unit test #2985 (see workaround)

For example, it converts this

import {createSignal} from 'solid-js'`

into this

import {createSignal} from './node_modules/solid-js/dist/dev.js'`

which defeats the purpose of the import map I have in place that loads Solid.js from CDN.

How do we disable all source transformation?