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/media_queries.rs

@@ -26,7 +26,7 @@ pub use gecko::media_queries::{Device, Expression};
 
 /// A type that encapsulates a media query list.
 #[derive(Clone, Debug)]
-#[cfg_attr(feature = "servo", derive(HeapSizeOf))]
+#[cfg_attr(feature = "servo", derive(MallocSizeOf))]
 pub struct MediaList {
     /// The list of media queries.
     pub media_queries: Vec<MediaQuery>,
@@ -48,7 +48,7 @@ impl MediaList {
 }
 
 /// <https://drafts.csswg.org/mediaqueries/#mq-prefix>
-#[cfg_attr(feature = "servo", derive(HeapSizeOf))]
+#[cfg_attr(feature = "servo", derive(MallocSizeOf))]
 #[derive(Clone, Copy, Debug, Eq, PartialEq, ToCss)]
 pub enum Qualifier {
     /// Hide a media query from legacy UAs:
@@ -63,7 +63,7 @@ pub enum Qualifier {
 ///
 /// [mq]: https://drafts.csswg.org/mediaqueries/
 #[derive(Clone, Debug, PartialEq)]
-#[cfg_attr(feature = "servo", derive(HeapSizeOf))]
+#[cfg_attr(feature = "servo", derive(MallocSizeOf))]
 pub struct MediaQuery {
     /// The qualifier for this query.
     pub qualifier: Option<Qualifier>,
@@ -135,7 +135,7 @@ impl ToCss for MediaQuery {
 
 /// <http://dev.w3.org/csswg/mediaqueries-3/#media0>
 #[derive(Clone, Debug, Eq, PartialEq)]
-#[cfg_attr(feature = "servo", derive(HeapSizeOf))]
+#[cfg_attr(feature = "servo", derive(MallocSizeOf))]
 pub enum MediaQueryType {
     /// A media type that matches every device.
     All,
@@ -164,7 +164,7 @@ impl MediaQueryType {
 
 /// <https://drafts.csswg.org/mediaqueries/#media-types>
 #[derive(Clone, Debug, Eq, PartialEq)]
-#[cfg_attr(feature = "servo", derive(HeapSizeOf))]
+#[cfg_attr(feature = "servo", derive(MallocSizeOf))]
 pub struct MediaType(pub CustomIdent);
 
 impl MediaType {