[gnome-shell-extension] How do I know what icons are available?

[xtranophilist aaa <xtranophilist gmail com>]

const St = imports.gi.St;
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this._icon = new St.Icon({ icon_name: 'fedora-logo-icon',
                                   icon_type: St.IconType.FULLCOLOR,
                                   icon_size: Main.panel.button.height });

This would make use of the 'fedora-logo-icon'. How do I know what
other icons are available to be used in similar way?