Improved TrustedQueryAPI signatures (#6129)

Changed returned type of API methods from `Result<bool,
xcm_runtime_apis::trusted_query::Error>` to a typed one `type
XcmTrustedQueryResult = Result<bool,
xcm_runtime_apis::trusted_query::Error>;`
Follow-up of
[PR-6039](https://github.com/paritytech/polkadot-sdk/pull/6039)

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Co-authored-by: Bastian Köcher <git@kchr.de>
Co-authored-by: Adrian Catangiu <adrian@parity.io>