Move non-gfx things out of `gfx_traits` and create a `base` crate (#32296)

For a long time, `gfx_traits` has held a lot of things unrelated to graphics
and also unrelated to the `gfx` crate (which is mostly about fonts).
This is a cleanup which does a few things:

1. Move non `gfx` crate things out of `gfx_traits`. This is important in
   order to prevent dependency cycles with a different integration between
   layout, script, and fonts.
2. Rename the `msg` crate to `base`. It didn't really contain anything
   to do with messages and instead mostly holds ids, which are used
   across many different crates in Servo. This new crate will hold the
   *rare* data types that are widely used.

Details:

 - All BackgroundHangMonitor-related things from base to a new
   `background_hang_monitor_api` crate.
 - Moved `TraversalDirection` to `script_traits`
 - Moved `Epoch`-related things from `gfx_traits` to `base`.
 - Moved `PrintTree` to base. This should be widely useful in Servo.
 - Moved `WebrenderApi` from `base` to `webrender_traits` and renamed it
   to `WebRenderFontApi`.

1 files changed, 1 insertions, 1 deletions

diff --git a/components/script/dom/servoparser/prefetch.rs b/components/script/dom/servoparser/prefetch.rs
index d11da362149..1f57ccc0a94 100644
--- a/components/script/dom/servoparser/prefetch.rs
+++ b/components/script/dom/servoparser/prefetch.rs
@@ -2,6 +2,7 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
 
+use base::id::PipelineId;
 use html5ever::buffer_queue::BufferQueue;
 use html5ever::tokenizer::states::RawKind;
 use html5ever::tokenizer::{
@@ -9,7 +10,6 @@ use html5ever::tokenizer::{
 };
 use html5ever::{local_name, Attribute, LocalName};
 use js::jsapi::JSTracer;
-use msg::constellation_msg::PipelineId;
 use net_traits::request::{CorsSettings, CredentialsMode, ParserMetadata, Referrer};
 use net_traits::{CoreResourceMsg, FetchChannels, IpcSend, ReferrerPolicy, ResourceThreads};
 use servo_url::{ImmutableOrigin, ServoUrl};