Allow simulation of messages without private key access

[jmrossy]

Currently, the simulate function isn't available on the StargateClient, only the SigningStargateClient. But signing clients require access to the key, which isn't always practical or possible.

I've been able to hack together a key-less version based on the signing client's simulate method but official support in the StargateClient would be preferable.

  const registry = new Registry([...defaultRegistryTypes, ...wasmTypes]);
  const encodedMsg = registry.encodeAsAny(message);
  const encodedPubkey = encodeSecp256k1Pubkey(Buffer.from(senderPubKey, 'hex'));
  const { sequence } = await stargateClient.getSequence(sender);
  const { gasInfo } = await stargateClient
    // @ts-ignore force access to protected method
    .forceGetQueryClient()
    .tx.simulate([encodedMsg], memo, encodedPubkey, sequence);
  const gasUnits = Uint53.fromString(gasInfo.gasUsed.toString()).toNumber();