Dac: Expose abstract dac hash

Context

Introduces Dac_hash which abstracts over the hash of Sc_rollup_reveal_hash.t. Dac_hash.t should be used in all places that operates on the protocol reveal hash. Closes: #4737 (closed)

Manually testing the MR

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
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