I'm not sure this is the right way to fix this. We should re-add the left hand margin on the buttonbar menus and top-level menus. That's consistent with what the context menu looks like, but more importantly it's also consistent with (at least) macOS.
This is a workaround until we have proper icons for menu.
What do you mean? The icons were removed, and are not coming back.
If we add the margin again then Menu doesn't look good with so much whitespace.
Maybe, but it's a standard design that we see elsewhere too - and consistency is good for usability.
If you like that way then I'm attaching the patch for the same which will add margins again as they were before icons.