Make Context.state type to {} by default

[LoicPoullain]

Issue

When using Context.state, if we forget to provide a value for the generic type, the property works as if it was of type any which is not type-safe.

Solution and steps

• Make Context.state default type to "{}" to make it necessary to provide a value for the generic type.

Checklist

• Add/update/check docs (code comments and docs/ folder).
• Add/update/check tests.
• Update/check the cli generators.