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/htmlinputelement.rs

@@ -62,7 +62,7 @@ const PASSWORD_REPLACEMENT_CHAR: char = '●';
 
 #[derive(Clone, Copy, JSTraceable, PartialEq)]
 #[allow(dead_code)]
-#[derive(HeapSizeOf)]
+#[derive(MallocSizeOf)]
 enum InputType {
     InputSubmit,
     InputReset,
@@ -93,7 +93,7 @@ pub struct HTMLInputElement {
     size: Cell<u32>,
     maxlength: Cell<i32>,
     minlength: Cell<i32>,
-    #[ignore_heap_size_of = "#7193"]
+    #[ignore_malloc_size_of = "#7193"]
     textinput: DomRefCell<TextInput<ScriptToConstellationChan>>,
     activation_state: DomRefCell<InputActivationState>,
     // https://html.spec.whatwg.org/multipage/#concept-input-value-dirty-flag
@@ -105,7 +105,7 @@ pub struct HTMLInputElement {
 
 #[derive(JSTraceable)]
 #[must_root]
-#[derive(HeapSizeOf)]
+#[derive(MallocSizeOf)]
 struct InputActivationState {
     indeterminate: bool,
     checked: bool,