Add shorthand ambient module definition for 'govuk-frontend'

[romaricpascal]

As govuk-frontend provides no types, TypeScript will type its exports as any but be unable to acknowledge fields inherited from parent classes. This leads to errors when trying to assign or use them.

TypeScript's shorthand ambient modules seem to also make inherited fields typed as any.

This "empty" module will override any other definition of the govuk-frontend module, either in another .d.ts file or in @types/govuk-frontend.

Issue was, our project was not configured to look up for .ts file, meaning any global.d.ts file was overlooked by TypeScript. Adding **/*.d.ts file to the tsconfig.json in src allows TypeScript to find the shorthand ambient module and TypeScript is happy with accessing this.$root in classes inheriting from Component 🥳

[netlify[bot]]

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