Fix UI regressions

[terryyylim]

Regressions

1. StepWizardHorizontal not being highlighted. Known issue mentioned here
2. Toasts not showing up after getting first Toast
   • dismissToast call is immediately made upon addition of a Toast to the global list
   • Likely because toast and toastToDismiss are the same because the subsequent Toast has the same id as the previous, instead of an unique one (https://github.com/elastic/eui/blob/main/src/components/toast/global_toast_list.tsx#L246)

UI Screenshots

[deadlycoconuts]

LGTM! 🚀 Thanks for fixing this! And thanks in advance when you'll cherry-pick this commit and apply it to the v1.6.1 tag :)