Investigate effects of enabling TypeScript's skipLibCheck

[romaricpascal]

What

Investigate if enabling TypeScript's skipLibCheck option helps avoid TypeScript throwing errors when dependencies have issues in the types they provide or their implementation. Ideally we'd want:

• not to error if a 3rd party dependency has type issues
• error if we misuses or have type issues amongst our own packages (eg. calling code from shared)

Especially:

• would we still be confident what we shipped is correctly typed?
• which kinds of errors would we open ourselves to in the future?

Why

We've now had several Dependabot PRs stuck because of type issues from 3rd parties, clogging our list of dependency updates over something we don't have control of:

• Bump the lint group across 1 directory with 5 updates #5542
• Bump the test group across 1 directory with 2 updates #5530 & Bump the test group across 1 directory with 4 updates govuk-design-system#4324
• Bump the lint group across 1 directory with 4 updates #5531

Who needs to work on this

Developers

Who needs to review this

Developers

Done when

• We understand what effects skipLibCheck has on our project
• We decided whether to enable it or not.