Implement XCM ExecuteWithOrigin instruction

[acatangiu]

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• This is not a support question.

Motivation

Right now, XCM has some good instructions for manipulating the origin during execution in same ways, like ClearOrigin and DescendOrigin.
However, these instructions are final, once you use them, there's no standard way of going back to the original origin.
This results in a complicated developer experience, where the order of operations needs to be highly taken into account to perform the operations needed, with the correct origins for each.

This new instruction, ExecuteWithOrigin, provides a way of executing a set of instructions with a particular origin.
It makes scenarios where multiple operations need to be performed by multiple origins much easier to do.
It gives a standard way of doing things like buying execution from a user's account and then returning to the previous origin to perform other operations that require the priviledges associated with it.
It also allows for previously impossible scenarios like acting on behalf of many sibling origins.

Request

Implement https://github.com/paritytech/xcm-format/blob/master/proposals/0038-execute-with-origin.md

Solution

Implement https://github.com/paritytech/xcm-format/blob/master/proposals/0038-execute-with-origin.md

Are you willing to help with this request?

Yes!