Bug 1943391 - Initial entrypoint to detect preview reqeust - r=Mardak,firefox-desktop-core-reviewers ,firefox-ai-ml-reviewers,mossop

- alt+hover to trigger LinkPreview
- add LinkPreview.sys.mjs modules
- disable browser.ml.linkPreview.enabled by default
- use setOverLink and LinkPreview.sys to handle keyboard shortcut
- dispatch CustomEvent OverLink from browser.js
- add/remove event listeners in sync with state of "browser.ml.linkPreview.enabled"
- update all_files_referenced to handle moz-src

Differential Revision: https://phabricator.services.mozilla.com/D239535

browser/base/content/browser.js

@@ -2359,6 +2359,12 @@ var XULBrowserWindow = {
    *   passed on to LinkTargetDisplay.
    */
   setOverLink(url, options = undefined) {
+    window.dispatchEvent(
+      new CustomEvent("OverLink", {
+        detail: { url },
+      })
+    );
+
     if (url) {
       url = Services.textToSubURI.unEscapeURIForUI(url);