light-client-verifier: 🌱 restore verify_commit() interface

in #1410, alterations to the `PredicateVerifier<P, C, V>` to improve
performance when verifying commits.

specifically, a call to
`verify_commit_against_trusted(untrusted, trusted, options)` will now
make use of new internal interfaces that check validator signatures and
signer overlap at the same time.

this is a worthwhile performance improvement, but in the process, it
made changes to the public interface of `PredicateVerifier<P, C, V>`
that break some use cases. as i understand it, there is no strict need
to remove the other public interface from the verifier. those that call
`verify_commit_against_trusted` can still receive a performance boost,
but calling `verify_commit` on just the untrusted state should still
work after those changes.

so, this commit restores `verify_commit(untrusted)`, and keeps
`verify_commit_against_trusted(untrusted, trusted, options)` under its
previous name.

light-client-verifier/src/verifier.rs

@@ -209,10 +209,24 @@ where
         Verdict::Success
     }
 
+    /// Verify that more than 2/3 of the validators correctly committed the block.
+    ///
+    /// Use [`PredicateVerifier::verify_commit_against_trusted()`] to also verify that there is
+    /// enough overlap between validator sets.
+    pub fn verify_commit(&self, untrusted: &UntrustedBlockState<'_>) -> Verdict {
+        verdict!(self.predicates.has_sufficient_signers_overlap(
+            untrusted.signed_header,
+            untrusted.validators,
+            &self.voting_power_calculator,
+        ));
+
+        Verdict::Success
+    }
+
     /// Verify that a) there is enough overlap between the validator sets of the
     /// trusted and untrusted blocks and b) more than 2/3 of the validators
     /// correctly committed the block.
-    pub fn verify_commit(
+    pub fn verify_commit_against_trusted(
         &self,
         untrusted: &UntrustedBlockState<'_>,
         trusted: &TrustedBlockState<'_>,
@@ -288,7 +302,7 @@ where
         ensure_verdict_success!(self.verify_validator_sets(&untrusted));
         ensure_verdict_success!(self.validate_against_trusted(&untrusted, &trusted, options, now));
         ensure_verdict_success!(self.check_header_is_from_past(&untrusted, options, now));
-        ensure_verdict_success!(self.verify_commit(&untrusted, &trusted, options));
+        ensure_verdict_success!(self.verify_commit_against_trusted(&untrusted, &trusted, options));
 
         Verdict::Success
     }
@@ -305,7 +319,7 @@ where
     ) -> Verdict {
         ensure_verdict_success!(self.verify_validator_sets(&untrusted));
         ensure_verdict_success!(self.validate_against_trusted(&untrusted, &trusted, options, now));
-        ensure_verdict_success!(self.verify_commit(&untrusted, &trusted, options));
+        ensure_verdict_success!(self.verify_commit_against_trusted(&untrusted, &trusted, options));
         Verdict::Success
     }
 }