witness: Add Witness::witness_script inspector

bitcoin/src/blockdata/witness.rs

@@ -450,6 +450,15 @@ impl Witness {
             }
         })
     }
+
+    /// Get the p2wsh witness script following BIP141 rules.
+    ///
+    /// This does not guarantee that this represents a P2WS [`Witness`]. See
+    /// [Script::is_p2wsh](crate::blockdata::script::Script::is_p2wsh) to
+    /// check whether this is actually a P2WSH witness.
+    pub fn witness_script(&self) -> Option<&Script> {
+        self.last().map(Script::from_bytes)
+    }
 }
 
 impl Index<usize> for Witness {