Change the button activation combo for Exit this Page to 3 x shift

[owenatgov]

What

Change the keypresses that activate the EtP button from the esc key 3 times in a given timeframe to shift 3 times.

As part of this, investigate ways to "clear" the press 3 times only when shift is intentionally pressed 3 times in a row, not accidentally eg: if using it in tandem with a letter key to capitalise a word/letters.

Why

This is a decision based on the outcomes of our spikes. See alphagov/govuk-design-system#2402 for more details.

Part of alphagov/govuk-design-system#1755

Who needs to work on this

Developers

Who needs to review this

Developers, Accessibility specialists

Done when

• We have a consistent way to activate the button using 3xshift that couldn't be activated accidentally
• This solution has been implemented into the EtP branch