Bug 1701108 - Create synthesized contextmenu event with button 2 ("eSecondary") to keep assertions happy. r=Gijs

We have a warning assertion that wants all contextmenu events to have button 2,
or be marked as a ctrl-click or triggered by the contextmenu keyboard key.
Fixing this avoids a warning in debug builds but is otherwise inconsequential.

Depends on D109825

Differential Revision: https://phabricator.services.mozilla.com/D109826

browser/base/content/nsContextMenu.js

@@ -86,7 +86,7 @@ function openContextMenu(aMessage, aBrowser, aActor) {
     false,
     false,
     false,
-    0,
+    2,
     null,
     0,
     context.mozInputSource