utils: add a few VecMap utility functions

libs/utils/src/vec_map.rs

@@ -20,10 +20,22 @@ impl<K: Ord, V> VecMap<K, V> {
         self.0.is_empty()
     }
 
+    pub fn last(&self) -> Option<&(K, V)> {
+        self.0.last()
+    }
+
     pub fn as_slice(&self) -> &[(K, V)] {
         self.0.as_slice()
     }
 
+    pub fn inner(self) -> Vec<(K, V)> {
+        self.0
+    }
+
+    pub fn len(&self) -> usize {
+        self.0.len()
+    }
+
     /// This function may panic if given a range where the lower bound is
     /// greater than the upper bound.
     pub fn slice_range<R: RangeBounds<K>>(&self, range: R) -> &[(K, V)] {
@@ -90,6 +102,10 @@ impl<K: Ord, V> VecMap<K, V> {
         Ok((None, delta_size))
     }
 
+    pub fn truncate(&mut self, pos: usize) {
+        self.0.truncate(pos)
+    }
+
     /// Split the map into two.
     ///
     /// The left map contains everything before `cutoff` (exclusive).