contracts: Change `define_env!` to expect a `Result<T, DispatchError>` for every function (#7762)

* Make host functions return TrapReason

This avoids the need to manually store any trap reasons
to the `Runtime` from the host function. This adds the following
benefits:

* It properly composes with the upcoming chain extensions
* Missing to set a trap value is now a compile error

* review: Remove superflous .into()