Refactor ProcessAttestationNoVerifySignature to VerifyAttestationNoVerifySignature

[terencechain]

What type of PR is this?

Refactor

What does this PR do? Why is it needed?

Currently

ProcessAttestationNoVerifySignature {
// Verify attestation slot, epoch... etc
// Modify beacon state with attestation
// Verify attestation valid indices
}

In Prysm, we use ProcessAttestationNoVerifySignature as a pure verification function without the advertised side effect as modifying beacon state. This PR changes:

VerifyAttestationNoVerifySignature {
// Verify attestation slot, epoch... etc
// Verify attestation valid indices
}

ProcessAttestationNoVerifySignature {
VerifyAttestationNoVerifySignature
// Modify beacon state with attestation
}

Note that Verify attestation valid indices now comes before Modify beacon state with attestation. That is ok and arguably better

Which issues(s) does this PR fix?

Helps #8563

Other notes for review

#8563 is blocked until this