Migrate example for invoking runtime from ink-types-node-runtime

[ascjones]

We should consider moving this example https://github.com/paritytech/ink-types-node-runtime/tree/master/examples/calls into this repo, in order to ensure it doesn't get out of date and to increase visibility.

It should not significantly increase CI times, which it has the potential to because it has some substrate dependencies. This can of course be mitigated with caching, but would need to be experimented with.

[Robbepop]

I would like to hear @TriplEight 's opinion on the feasibility of this.

[TriplEight]

It will not seriously affect CI times of this repo, please go ahead with migration.

[cmichi]

I just stumbled upon this ticket.

Summary:

• This functionality should currently be implemented via chain extensions.
• There is an unstable API call_runtime in pallet-contracts, which will enable this in the future.
• The function signature of it will change though.
• Let's wait until the function call_runtime is stabilized before tackling this issue.