`sc-chain-spec`: add support for custom host functions (#2190)
Genesis building in runtime may involve calling some custom host functions. This PR allows to pass `HostFunctions` into the `ChainSpec` struct, which in turn are passed to `WasmExecutor`. The `ChainSpec` now has extended host functions type parameter: ``` pub struct ChainSpec<G, E = NoExtension, EHF = ()> ``` which will be combined with the default set (`sp_io::SubstrateHostFunctions`) in an instance of `WasmExecutor` used to build the genesis config. Fix for #2188 --------- Co-authored-by: Davide Galassi <[email protected]> Co-authored-by: Bastian Köcher <[email protected]>