Replace all uses of the heapsize crate with malloc_size_of.

Servo currently uses `heapsize`, but Stylo/Gecko use `malloc_size_of`.
`malloc_size_of` is better -- it handles various cases that `heapsize` does not
-- so this patch changes Servo to use `malloc_size_of`.

This patch makes the following changes to the `malloc_size_of` crate.

- Adds `MallocSizeOf` trait implementations for numerous types, some built-in
  (e.g. `VecDeque`), some external and Servo-only (e.g. `string_cache`).

- Makes `enclosing_size_of_op` optional, because vanilla jemalloc doesn't
  support that operation.

- For `HashSet`/`HashMap`, falls back to a computed estimate when
  `enclosing_size_of_op` isn't available.

- Adds an extern "C" `malloc_size_of` function that does the actual heap
  measurement; this is based on the same functions from the `heapsize` crate.

This patch makes the following changes elsewhere.

- Converts all the uses of `heapsize` to instead use `malloc_size_of`.

- Disables the "heapsize"/"heap_size" feature for the external crates that
  provide it.

- Removes the `HeapSizeOf` implementation from `hashglobe`.

- Adds `ignore` annotations to a few `Rc`/`Arc`, because `malloc_size_of`
  doesn't derive those types, unlike `heapsize`.

components/script/dom/testbinding.rs

@@ -723,9 +723,9 @@ impl TestBindingMethods for TestBinding {
         p.append_native_handler(&handler);
         return p;
 
-        #[derive(HeapSizeOf, JSTraceable)]
+        #[derive(JSTraceable, MallocSizeOf)]
         struct SimpleHandler {
-            #[ignore_heap_size_of = "Rc has unclear ownership semantics"]
+            #[ignore_malloc_size_of = "Rc has unclear ownership semantics"]
             handler: Rc<SimpleCallback>,
         }
         impl SimpleHandler {
@@ -804,9 +804,9 @@ impl TestBinding {
     pub unsafe fn condition_unsatisfied(_: *mut JSContext, _: HandleObject) -> bool { false }
 }
 
-#[derive(HeapSizeOf, JSTraceable)]
+#[derive(JSTraceable, MallocSizeOf)]
 pub struct TestBindingCallback {
-    #[ignore_heap_size_of = "unclear ownership semantics"]
+    #[ignore_malloc_size_of = "unclear ownership semantics"]
     promise: TrustedPromise,
     value: DOMString,
 }