Fix lc execution header bug

[Inspector-Butters]

This should be reviewed after #14457 is merged.

What type of PR is this?
Bug fix

What does this PR do? Why is it needed?
This PR fixes a bug in core/light-client where the update.AttestedHeader.Execution and update.AttestedHeader.ExecutionBranch were being created based on current Block and not AttestedBlock.

specifically:

• Adds tests for checking the AttestedHeader.Execution and AttestedHeader.ExecutionBranch.
• Adds the AttestedBlock input parameter to the CreateNewLightClientUpdate, CreateNewLightClientOptimisticUpdate, and CreateNewLightClientFinalityUpdate in the core/light-client.
• Adds the AttestedBlock input parameter to the same functions above, but in RPC/eth/light-client.
• Passes the AttestedBlock from the LC handlers through to the core package.
• Defines and uses the BlockToLightClientHeader function instead of calculating the headers manually in core/light-client
• And generally applies the consensus specs to the CreateNewLightClientUpdate function.

Which issues(s) does this PR fix?
This PR is needed as part of #12991