Move @lingui/core to regular dependencies

[tkers]

This commit https://github.com/contentful/field-editors/commit/f2ece016d3062427de17e5ad51838fb85150213d seems to introduce a (non-dev) dependency to @lingui/core, but the package.json file was not updated to reflect that, causing this module to break in production builds where devDependencies are not installed.

Update: Might want to look at a different solution as I see @lingui/core listed as peer dependency, but prior to the latest patch this was not an actual requirement.

[github-actions[bot]]

Marking pull request as stale since there was no activity for 30 days