XCM: Remote account converter (#6662)

* Draft remote account converter

* Tests and doc comments

* Adapt naming, tests fix

* Try with prefix in account

* Revert "Try with prefix in account"

This reverts commit 461759794cc9f59f768aad0e0899df6dc8cba747.

* Adapt code and test to review suggestions

* adapt to take into account parent in conversion

* fix: docs

* fix: try doc fix v2