Auto-generate the GetWeight impl for the XCM Instruction enum

[bolajahmad]

Description

Closes #12279.

Define a custom macro to autogenerate WeightInfo implementations for Instruction.

Integration

No special integration is needed. While the XcmWeightInfo is used by runtimes of rococo/westend/cumulus, this PR is unexpected to break these implementations as this is an optimization and refactoring issue.

Review Notes

This PR deleted a manual code block and uses the same xcm_procedural::XcmWeightInfoTrait that generates the WeightInfo trait to also generate the implementations also. In future updates, nothing else needs to be done as every new Instruction will be autogenerated.

This implementation includes a unit test to prevent regression logic when using the XcmWeightInfo.

Include your leftover TODOs, if any, here.

• Ensure regression can be detected immediately

Checklist

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