Usage of TS modules seems outdated

[stepanh]

Hi,

I understand that syntax like export module Util { in packages/core/src/util/index.ts is outdated as per this eslint rule:
Use 'namespace' instead of 'module' to declare custom TypeScript
modules.eslint@typescript-eslint/prefer-namespace-keyword

Maybe it would be best to not use namespaces/modules at all? I would be happy to do a PR.