Cross-contract call tracing

[pmikolajczyk41]

We make use of the recent extension to pallet-contracts, which enables tracing cross-contract calls.

[deuszx]

Left a couple of comments. In general, code looks confusing (which in Substrate usually means good) but the example usage (test) is not very useful.

[deuszx]

I'd prefer to see a test where DebugExtT::after_call is used to extract some data from the after_call trace (and before_call as well) which is then used to make some assertions in the unit test itself. I think an example like that would be far more useful for future users of this tracing feature.

[pmikolajczyk41]

this would require interpreting Values from input_data :|