Upgrade to eslint 9, use flat config

[patrickpatrickpatrick]

Fixes alphagov/govuk-design-system#3649

[github-actions]

📋 Stats

File sizes

File	Size
dist/govuk-frontend-development.min.css	118.41 KiB
dist/govuk-frontend-development.min.js	42.93 KiB
packages/govuk-frontend/dist/govuk/all.bundle.js	91.34 KiB
packages/govuk-frontend/dist/govuk/all.bundle.mjs	85.77 KiB
packages/govuk-frontend/dist/govuk/all.mjs	1.18 KiB
packages/govuk-frontend/dist/govuk/govuk-frontend-component.mjs	1.74 KiB
packages/govuk-frontend/dist/govuk/govuk-frontend.min.css	118.4 KiB
packages/govuk-frontend/dist/govuk/govuk-frontend.min.js	42.92 KiB
packages/govuk-frontend/dist/govuk/i18n.mjs	5.55 KiB
packages/govuk-frontend/dist/govuk/init.mjs	6.85 KiB

Modules

File	Size (bundled)	Size (minified)
all.mjs	81.9 KiB	40.37 KiB
accordion.mjs	25.46 KiB	12.93 KiB
button.mjs	7.96 KiB	3.31 KiB
character-count.mjs	24.39 KiB	10.5 KiB
checkboxes.mjs	7.81 KiB	3.42 KiB
error-summary.mjs	9.87 KiB	4.07 KiB
exit-this-page.mjs	19.08 KiB	9.86 KiB
header.mjs	6.46 KiB	3.22 KiB
notification-banner.mjs	8.24 KiB	3.23 KiB
password-input.mjs	17.13 KiB	7.86 KiB
radios.mjs	6.81 KiB	2.98 KiB
service-navigation.mjs	6.44 KiB	3.26 KiB
skip-link.mjs	6.4 KiB	2.76 KiB
tabs.mjs	12.04 KiB	6.67 KiB

View stats and visualisations on the review app

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