[ic-toggle-button-group]: Setting the `iconPlacement` on `<ic-toggle-button-group>` doesn't affect the icon placement on `<ic-toggle-button>`

[GCHQ-Developer-112]

Summary of the bug

Setting the iconPlacement on <ic-toggle-button-group> doesn't affect the icon placement on <ic-toggle-button>. If no iconPlacement is set on <ic-toggle-button>, then it defaults to a left icon placement. This overrides the iconPlacement set on <ic-toggle-button-group> and so setting the iconPlacement prop on <ic-toggle-button-group> is ineffective. In order to have the desired iconPlacement, it always needs to be set on the <ic-toggle-button>. To fix this issue whilst ensuring that the default iconPlacement is always left, setting iconPlacement on <ic-toggle-button-group> should override the iconPlacement set on each individual <ic-toggle-button>.

📸 Screenshots or code

🧐 Expected behaviour

Setting iconPlacement on <ic-toggle-button-group> should override the iconPlacement set on each individual <ic-toggle-button>.