When constructing XCM Transact calls, it's useful to have an idea of how much weight some call will consume and how much that weight will cost in order to BuyExecution. query_info only takes a fully encoded extrinsic and returns the weight and fee, but requires some hacks, namely:

• Users must add some bytes to represent an extrinsic (signature/signed extensions), but an XCM Transact will just have the call.
• The return includes the length fee and the ExtrinsicBaseWeight, which are not relevant in Transact.

The addition of these two endpoints would allow submission of a Call and obtaining its weight and a fee estimate (with the user knowing that the weight to fee rate can be variable so they'll want to supply a little extra):

• fn get_dispatch_info(call) -> DispatchInfo { weight, ... }; (useful for specifying required weight)
• fn weight_to_fee(weight) -> Balance; (useful for buying execution)

Related: polkadot-js/apps#7688