Revisit soundness of timestmp inherent in parachain context

[JoshOrndorff]

The big question here is What guarantees can parachain runtime's rely on the relay chain validators to enforce with regards to inherent data.

I like the timestamp example because it is concrete. Is it sound for a parachain to have it's own timestamp inherent? You don't want the relay chain validators to accept a block that the collators will reject because of a bad timestamp.

I argue that Tuxedo should offer the parachain runtime the guarantee that its inherents will be valid.

This issue is to assess whether Tuxedo is doing that, and if not to start doing that.
And more broadly, this issue to to follow up with the Substrate community and the FRAME developers to see whether FRAME is doing this correctly.

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Relevant Cumulus PR and SE question.

paritytech/cumulus#2658

[JoshOrndorff]

Moonbeam is still using the check inherents feature https://github.com/moonbeam-foundation/moonbeam/blob/96cf8898874509d529b03c4da0e07b2787bacb18/runtime/moonbeam/src/lib.rs#L1584C1-L1606C2.

My reach goal would be to basically have the ParachainConstraintChecker trait have another function called fn get_inherent_data_for_checking_inherents(...) -> InherentData. Then impl it similarly to how moonbeam does.

One open question is what exactly goes in the parameters. Maybe block and relay_chain_state_proof.