`open-menu-symbolic` should be three lines or three dots instead of a gear

### What Happened?

The gear for `open-menu-symbolic` (also used as `application-menu-symbolic`) is misleading, as it express settings instead of an actions menu.

For example for Flatseal, on Gnome, the menu icon looks like this:

when in Elementary, it looks like that:

This page describes why Gnome changed from using a gear icon to the three lines icon: https://wiki.gnome.org/Initiatives(2f)GnomeGoals(2f)GearIcons.html. I think Elementary should apply the same logic.

Other Desktop environments use a three dots icon. `view-more-symbolic` () could also be used as `open-menu-symbolic`.

### Steps to Reproduce

Launch a GTK app using `open-menu-symbolic` icon, like Flatseal, ~Warehouse~ or Main Menu.

### Expected Behavior

The `open-menu-symbolic` icon should express that it contains actions, not settings. To this effect, an "hamburger" style icon would be better than a "gear" one.

### OS Version

8.x (Circe)

### OS Architecture

amd64

### Session Type

Classic Session (X11, This is the default)

### Software Version

Latest release (I have run all updates)