message: add a helper function for querying supply
diff: @@ -18,6 +18,7 @@ use crate::query::{
  };
  use crate::results::{ContractResult, Empty, SystemResult};
  use crate::serde::{from_binary, to_binary, to_vec};
  +use crate::SupplyResponse;
  /// Storage provides read and write access to a persistent storage.
  /// If you only want to provide read access, provide `&Storage`
  @@ -197,6 +198,15 @@ impl<'a, C: CustomQuery> QuerierWrapper<'a, C> {
  }
  }
  + pub fn query_supply(&self, denom: impl Into<String>) -> StdResult<Coin> {
  + let request = BankQuery::Supply {
  + denom: denom.into(),
  + }
  + .into();
  + let res: SupplyResponse = self.query(&request)?;
  + Ok(res.amount)
  + }
  +
  pub fn query_balance(
  &self,
  address: impl Into<String>,
  