collab: Make the join link work regardless of user preferences

veaction=editsource/edit links always work, even if you have the
visual editor disabled in preferences or if you're using different
default mode than the session host.

Bug: T370817
Change-Id: Ia4a72cdbdd732a29fd353a5efa6ee912d32374cb

Author: MatmaRex

collab/ve.ui.CollabProcessDialog.js

@@ -145,6 +145,9 @@ ve.ui.HostCollabProcessDialog.prototype.onButtonClick = function () {
 
 	ve.collab.initPeerServer( this.userNameInput.getValue() );
 	const collabUrl = new URL( location.href );
+	collabUrl.searchParams.delete( 'action' );
+	collabUrl.searchParams.set( 'veaction',
+		ve.init.target.getSurface().getMode() === 'source' ? 'editsource' : 'edit' );
 	ve.collab.peerServer.peer.on( 'open', ( newId ) => {
 		collabUrl.searchParams.set( 'collabSession', newId );
 		this.copyTextLayout.textInput.setValue( collabUrl );