feat(defaults): popupmenu "Open in browser", "Go to definition" #30261

- Use the popup to expose more features such as LSP and gx.
- Move the copy/paste items lower in the menu, they are lower priority.

test/functional/ui/multigrid_spec.lua

@@ -1095,6 +1095,7 @@ describe('ext_multigrid', function()
   end)
 
   it('supports mouse', function()
+    command('autocmd! nvim_popupmenu') -- Delete the default MenuPopup event handler.
     insert('some text\nto be clicked')
     screen:expect{grid=[[
     ## grid 1