make Term::as_slice public (#1846)

src/schema/term.rs

@@ -375,7 +375,7 @@ where B: AsRef<[u8]>
     ///
     /// Do NOT rely on this byte representation in the index.
     /// This value is likely to change in the future.
-    pub(crate) fn as_slice(&self) -> &[u8] {
+    pub fn as_slice(&self) -> &[u8] {
         self.0.as_ref()
     }
 }