Implement the Tudor crown favicons (v4.x)

[querkmachine]

Implements the Tudor crown for browser 'favourite' icons, homescreen icons and OpenGraph sharing graphics whilst maintaining the same set of formats provided in prior v4 releases. Part of #4179.

Warning

This PR should not be merged until we have approval to do so.

Changes

• Replaces icons using the St. Edward's crown with equivalents using the Tudor crown.
• Redesigns the smallest icon sizes (48px and below) to use a simplified version of the Tudor crown icon.
• Inverts the design of the mask icon to be consistent with how the icon is presented elsewhere. The crown is now transparent and presented within a coloured box.

Assets included

Name	Type	Dimensions	Notes
Icon container favicon.ico	Icon container	16×16, 32×32, 48×48	Multiple PNGs bundled into a single container. All images use simplified crown design. Primarily used by Safari (iOS/iPadOS), IE and some third-parties.
Apple touch icon (120) govuk-apple-touch-icon.png	PNG	120×120	Primarily used on the iOS homescreen on iPhones with @2x retina displays. May also be used by Android devices.
Apple touch icon (152) govuk-apple-touch-icon-152.png	PNG	152×152	Primarily used on the homescreen of iPads and iPad minis. May also be used by Android devices.
Apple touch icon (167) govuk-apple-touch-icon-167.png	PNG	167×167	Primarily used on the homescreen of iPad Pros. May also be used by Android devices.
Apple touch icon (180) govuk-apple-touch-icon-180.png	PNG	180×180	Primarily used on the iOS homescreen on iPhones with @3x retina displays. May also be used by Android devices and docked webpages in macOS Sonoma.
Mask icon govuk-mask-icon.svg	SVG	variable	Uses simplified crown design. Primarily used by Safari (macOS) and MacBooks featuring the Touch Bar.
OpenGraph image govuk-opengraph-image.png	PNG	1200×630	Primarily used when sharing on third-party websites and services.

[querkmachine]

Merging in preparation for release w/c 15th January.