feat(acir)!: replace MerkleMembership opcode with ComputeMerkleRoot

[TomAFrench]

Related issue(s)

Resolves #25

Description

Summary of changes

This PR updates the name of the MerkleMembership opcode to ComputeMerkleRoot. This signals that this opcode will begin to return the merkle root rather than a boolean flag for whether the passed value for the root matches the calculated value.

aztec_backend is ready to switch over to use ComputeMerkleRoot noir-lang/acvm-backend-barretenberg#143 so we can make this change and begin propagating it up to noir.

Dependency additions / changes

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Test additions / changes

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Checklist

• I have tested the changes locally.
• I have formatted the changes with Prettier and/or cargo fmt with default settings.
• I have linked this PR to the issue(s) that it resolves.
• I have reviewed the changes on GitHub, line by line.
• I have ensured all changes are covered in the description.

Additional context

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