Disable incorrect iOS/Edge text size adjustments

[colinrotherham]

To cater for non-responsive "desktop only" websites, iPhone OS launched with a feature to increase the text size automatically so it was more legible:

To prevent font size tampering, it can be turned off with:

html {
    -webkit-text-size-adjust: 100%;
}

It's also supported by:

1. Windows Phone 8.1
2. Windows 10 Mobile
3. Microsoft Edge

In Edge, it appears to kick in for portrait tablet mode on smaller non-pro Microsoft Surfaces.

Since GOV.UK Frontend already takes care of typography, we should opt out of this as shown:

Before

19px text in .govuk-list has been "boosted" to 25px (auto sizing)

After

19px text .govuk-list remains correctly at 19px (set to 100%)

Also found in CSS resets (normalize.css, Bootstrap) and prevents the subtle "zoom in" when rotated.

[36degrees]

It looks like this does exist in GOV.UK Template, but wasn't bought through.

Gets a thumbs up from me – thanks @colinrotherham.

We just need another approval from someone else on the team and then we can merge this.

[NickColley]

Really good PR thanks Colin 👏