`xcm`: Change `TypeInfo::path` to not include `staging` (#1948)

The `xcm` crate was renamed to `staging-xcm` to be able to publish it to
crates.io as someone as squatted `xcm`. The problem with this rename is
that the `TypeInfo` includes the crate name which ultimately lands in
the metadata. The metadata is consumed by downstream users like
`polkadot-js` or people building on top of `polkadot-js`. These people
are using the entire `path` to find the type in the type registry. Thus,
their code would break as the type path would now be [`staging_xcm`,
`VersionedXcm`] instead of [`xcm`, `VersionedXcm`]. This pull request
fixes this by renaming the path segment `staging_xcm` to `xcm`.

This requires: https://github.com/paritytech/scale-info/pull/197



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Co-authored-by: Francisco Aguirre <[email protected]>