Lift/lower refactors inspired by map<K, V> (#12753)

In reading over #12216 I found a few related but also somewhat
orthogonal refactors that I wanted to implement, and thus this commit.
Changes here are:

* Handling pointer pairs for lists/maps/strings is now more uniform with
  a single set of functions doing the lift/lower to flat/memory. Less
  "FIXME 4311" spread throughout effectively.

* Conditional defines and organization of the `HashMap`-related impls
  were tweaked, for example impls on `HashMap` are now unconditional as
  well as `TryHashMap`. Some internals were refactored to in theory
  reduce complexity, but this is also subjective.

* Lifting a `map<K, V>` now consumes fuel, a recent change, to ensure
  that resource exhaustion in the host is limited.

Author: alexcrichton

crates/environ/src/collections/hash_map.rs

@@ -252,3 +252,9 @@ impl<K, V, S> IntoIterator for TryHashMap<K, V, S> {
         self.inner.into_iter()
     }
 }
+
+impl<K, V, S> From<TryHashMap<K, V, S>> for inner::HashMap<K, V, S> {
+    fn from(map: TryHashMap<K, V, S>) -> Self {
+        map.inner
+    }
+}