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/style/values/computed/angle.rs

@@ -14,9 +14,8 @@ use values::distance::{ComputeSquaredDistance, SquaredDistance};
 
 /// A computed angle.
 #[animate(fallback = "Self::animate_fallback")]
-#[cfg_attr(feature = "gecko", derive(MallocSizeOf))]
-#[cfg_attr(feature = "servo", derive(HeapSizeOf, Deserialize, Serialize))]
-#[derive(Animate, Clone, Copy, Debug, PartialEq)]
+#[cfg_attr(feature = "servo", derive(Deserialize, Serialize))]
+#[derive(Animate, Clone, Copy, Debug, MallocSizeOf, PartialEq)]
 #[derive(PartialOrd, ToAnimatedZero)]
 pub enum Angle {
     /// An angle with degree unit.