Fix EditorJS default import types for Node16

[cyphercodes]

Summary

• add conditional package exports so Node16/NodeNext import resolution can use an ESM declaration entrypoint
• add an index.d.mts wrapper that keeps the default EditorJS export constructable while preserving existing named type/value exports
• add a type fixture covering default construction with moduleResolution: Node16

Fixes #2624.

Verification

• yarn install --frozen-lockfile --ignore-scripts --ignore-engines
• yarn test:types
• npx -y -p typescript@5.9.3 tsc -p test/types/tsconfig.node16.json --pretty false
• npx -y -p typescript@5.9.3 tsc -p test/types/tsconfig.node16.json --module NodeNext --moduleResolution NodeNext --pretty false
• yarn lint:errors
• yarn build
• git diff --check