toml: add Map::retain method

crates/toml/src/map.rs

@@ -138,6 +138,20 @@ impl Map<String, Value> {
         self.map.remove(key)
     }
 
+    /// Retains only the elements specified by the predicate.
+    ///
+    /// In other words, remove all pairs `(k, v)` such that `f(&k, &mut v)` returns
+    /// `false`.
+    ///
+    /// The elements are visited in iteration order.
+    #[inline]
+    pub fn retain<F>(&mut self, keep: F)
+    where
+        F: FnMut(&String, &mut Value) -> bool,
+    {
+        self.map.retain(keep);
+    }
+
     /// Gets the given key's corresponding entry in the map for in-place
     /// manipulation.
     pub fn entry<S>(&mut self, key: S) -> Entry<'_>