compositing: Add memory reporter for WebRender. (#36557)

This adds a memory reporter for WebRender's memory usage. I seeded it
with a couple entries that looked reasonable based on
https://searchfox.org/mozilla-central/rev/2c71f1e9b5947612abdc16b64008162c58c1b9d3/gfx/thebes/gfxPlatform.cpp#722-738.

Testing: Verified that new numbers appear in about:memory for servo.org.
The new images category is surprisingly large (40mb).

Signed-off-by: Josh Matthews <josh@joshmatthews.net>

Cargo.lock

@@ -1106,6 +1106,7 @@ dependencies = [
  "pixels",
  "profile_traits",
  "script_traits",
+ "servo_allocator",
  "servo_config",
  "servo_geometry",
  "stylo_traits",
@@ -1114,6 +1115,7 @@ dependencies = [
  "webrender",
  "webrender_api",
  "webxr",
+ "wr_malloc_size_of",
 ]
 
 [[package]]
@@ -1132,6 +1134,7 @@ dependencies = [
  "ipc-channel",
  "log",
  "pixels",
+ "profile_traits",
  "raw-window-handle",
  "serde",
  "servo_geometry",
@@ -4353,6 +4356,7 @@ dependencies = [
  "servo-media",
  "servo-media-dummy",
  "servo-media-gstreamer",
+ "servo_allocator",
  "servo_config",
  "servo_geometry",
  "servo_url",