Use Gulp to copy files instead of cpy

[colinrotherham]

Adding a dash of Gulp back again 😶

Closes #4439 by replacing our files.copy() task with gulp.src() + gulp.dest()

Removing the cpy package

This lets us remove the cpy package added in 8edda31 due to the maintainer stating:

IMPORTANT: This package has a lot of problems and I unfortunately don't have time to fix them. I would recommend against using this package until these problems are resolved. Help welcome (see the issue tracker) 🙏

[github-actions]

📋 Stats

File sizes

File	Size
dist/govuk-frontend-development.min.css	113.72 KiB
dist/govuk-frontend-development.min.js	38.54 KiB
packages/govuk-frontend/dist/govuk/all.bundle.js	78.3 KiB
packages/govuk-frontend/dist/govuk/all.bundle.mjs	73.58 KiB
packages/govuk-frontend/dist/govuk/all.mjs	3.86 KiB
packages/govuk-frontend/dist/govuk/govuk-frontend-component.mjs	359 B
packages/govuk-frontend/dist/govuk/govuk-frontend.min.css	113.7 KiB
packages/govuk-frontend/dist/govuk/govuk-frontend.min.js	38.53 KiB
packages/govuk-frontend/dist/govuk/i18n.mjs	5.38 KiB

Modules

File	Size
all.mjs	69.9 KiB
components/accordion/accordion.mjs	21.67 KiB
components/button/button.mjs	4.7 KiB
components/character-count/character-count.mjs	21.24 KiB
components/checkboxes/checkboxes.mjs	5.83 KiB
components/error-summary/error-summary.mjs	6.09 KiB
components/exit-this-page/exit-this-page.mjs	16.08 KiB
components/header/header.mjs	3.9 KiB
components/notification-banner/notification-banner.mjs	4.54 KiB
components/radios/radios.mjs	4.83 KiB
components/skip-link/skip-link.mjs	4.3 KiB
components/tabs/tabs.mjs	9.66 KiB

View stats and visualisations on the review app

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Action run for 50f0515

[romaricpascal]

Cheers for sorting this out 🙌🏻