Add gas limit estimation to typescript library

[corverroos]

Problem to Solve

Developers need to specify a gas limit for an xmsg. If they submit too low, it fails, if they submit too high, they overpay. We should make it easy to estimate the expected gas limit. This can be parameterized and submitted by a user, but this is currently difficult to do because there is no easy way to simulate how much a an xmsgs will cost.

Proposed Solution

Add the ability to compute the expected gas limit of an XMsg on a destination chain in a typescript library.

[arajasek]

Note: Part of the bigger effort of typescript tooling, we need to work on this during Public Omega in order to have ready for Mainnet.