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, 15 insertions, 6 deletions

diff --git a/components/shared/script/script_msg.rs b/components/shared/script/script_msg.rs
index a51859231ba..d750d33340d 100644
--- a/components/shared/script/script_msg.rs
+++ b/components/shared/script/script_msg.rs
@@ -5,18 +5,18 @@
 use std::collections::{HashMap, VecDeque};
 use std::fmt;
 
+use base::id::{
+    BroadcastChannelRouterId, BrowsingContextId, HistoryStateId, MessagePortId,
+    MessagePortRouterId, PipelineId, ServiceWorkerId, ServiceWorkerRegistrationId,
+    TopLevelBrowsingContextId,
+};
+use base::Epoch;
 use canvas_traits::canvas::{CanvasId, CanvasMsg};
 use devtools_traits::{ScriptToDevtoolsControlMsg, WorkerId};
 use embedder_traits::{EmbedderMsg, MediaSessionEvent};
 use euclid::default::Size2D as UntypedSize2D;
 use euclid::Size2D;
-use gfx_traits::Epoch;
 use ipc_channel::ipc::{IpcReceiver, IpcSender};
-use msg::constellation_msg::{
-    BroadcastChannelRouterId, BrowsingContextId, HistoryStateId, MessagePortId,
-    MessagePortRouterId, PipelineId, ServiceWorkerId, ServiceWorkerRegistrationId,
-    TopLevelBrowsingContextId, TraversalDirection,
-};
 use net_traits::request::RequestBuilder;
 use net_traits::storage_thread::StorageType;
 use net_traits::CoreResourceMsg;
@@ -492,3 +492,12 @@ pub enum SWManagerMsg {
     /// <https://github.com/servo/servo/issues/24660>
     PostMessageToClient,
 }
+
+/// The direction of a history traversal
+#[derive(Clone, Copy, Debug, Deserialize, Eq, Hash, PartialEq, Serialize)]
+pub enum TraversalDirection {
+    /// Travel forward the given number of documents.
+    Forward(usize),
+    /// Travel backward the given number of documents.
+    Back(usize),
+}