Import maps broke webextensions support

[Mubelotix]

PR #10073 added support for importmaps. It adds inline scripts in html, looking like this.

<script type=importmap>{"imports":{"1QvWx":"/vitesse-dark.fcff75b4.js","h2sSK":"/vitesse-light.a1f9395b.js","xlGfb":"/javascript.ae5047f7.js"}}</script>

However, this broke Parcel's support for webextensions as this behavior cannot be disabled and inline scripts are disabled in web extension pages. The CSP is too strict and while Chrome and Firefox will allow sha256 whitelists to be added, Edge and other implementations stricly deny inline scripts. They will not change. We won't ever be able to add inline scripts.

We need a way to disable import maps.