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/generics/transform.rs

@@ -10,9 +10,7 @@ use values::CSSFloat;
 
 /// A generic 2D transformation matrix.
 #[allow(missing_docs)]
-#[cfg_attr(feature = "gecko", derive(MallocSizeOf))]
-#[cfg_attr(feature = "servo", derive(HeapSizeOf))]
-#[derive(Clone, Copy, Debug, PartialEq, ToComputedValue, ToCss)]
+#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, ToComputedValue, ToCss)]
 #[css(comma, function)]
 pub struct Matrix<T, U = T> {
     pub a: T,
@@ -24,10 +22,8 @@ pub struct Matrix<T, U = T> {
 }
 
 /// A generic transform origin.
-#[cfg_attr(feature = "gecko", derive(MallocSizeOf))]
-#[cfg_attr(feature = "servo", derive(HeapSizeOf))]
 #[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug)]
-#[derive(PartialEq, ToAnimatedZero, ToComputedValue, ToCss)]
+#[derive(MallocSizeOf, PartialEq, ToAnimatedZero, ToComputedValue, ToCss)]
 pub struct TransformOrigin<H, V, Depth> {
     /// The horizontal origin.
     pub horizontal: H,
@@ -40,9 +36,7 @@ pub struct TransformOrigin<H, V, Depth> {
 /// A generic timing function.
 ///
 /// <https://drafts.csswg.org/css-timing-1/#single-timing-function-production>
-#[cfg_attr(feature = "gecko", derive(MallocSizeOf))]
-#[cfg_attr(feature = "servo", derive(HeapSizeOf))]
-#[derive(Clone, Copy, Debug, PartialEq)]
+#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq)]
 pub enum TimingFunction<Integer, Number> {
     /// `linear | ease | ease-in | ease-out | ease-in-out`
     Keyword(TimingKeyword),