This PR bumps the Typescript version used on Kibana into v5.1.6. The full set of changes can be found here and here.
In order to make assumptions over the codebase and all the type of errors I choose to mark the failures with @ts-expect-error and let each team decide how to handle it.
Summary
From https://github.com/elastic/kibana/pull/186437:
Our team's list of changes: