Reduce Wasm Code Size Impact of Host Trait

[rauljordan]

Description

After this PR, the code impact of the Host trait addition on contracts is only 0.1Kb compared to the code from 0.7.0.

Using global functions that take in a &dyn Trait has a massive impact on WASM size, compared to instead implementing the method as a trait on your contract. Here’s the context:
We have a Contract struct in Rust, and we have a Router trait we are required to implement. Looks a bit like this today:

We route each selector to a specific method of our contract struct, and before that, we check if we need to deny non-payable functions that have a tx with a value

The problem is this deny_value method takes in a &dyn Host, which requires the compiler to produce more data to resolve vtables
We fixed this by instead defining a ValueDenier trait that contracts implement, so there is no need for a global deny_value method. Here is

the fix, which has 0 impact on wasm size compared to 2Kb from the prior screenshots

[gligneul]

Great find!