Add aria-hidden attribute to banner, set tabindex on all links, buttons, inputs inside banner

Neil Blairrequested to merge
issue/eu_cookie_compliance-3298345:3298345-withdraw-banner-keyboard-focus-2 into 8.x-1.x

Add aria-hidden attribute to banner and set tabindex on all links, buttons and inputs when banner shown or hidden

Closes #3298345

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