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`.

components/compositing/Cargo.toml

@@ -16,6 +16,7 @@ default = []
 multiview = []
 
 [dependencies]
+base = { workspace = true }
 canvas = { path = "../canvas" }
 compositing_traits = { workspace = true }
 crossbeam-channel = { workspace = true }
@@ -30,7 +31,6 @@ ipc-channel = { workspace = true }
 keyboard-types = { workspace = true }
 libc = { workspace = true }
 log = { workspace = true }
-msg = { workspace = true }
 net_traits = { workspace = true }
 pixels = { path = "../pixels" }
 profile_traits = { workspace = true }

components/compositing/compositor.rs

@@ -11,6 +11,8 @@ use std::iter::once;
 use std::rc::Rc;
 use std::time::{Duration, Instant, SystemTime, UNIX_EPOCH};
 
+use base::id::{PipelineId, TopLevelBrowsingContextId, WebViewId};
+use base::{Epoch, WebRenderEpochToU16};
 use canvas::canvas_paint_thread::ImageUpdate;
 use compositing_traits::{
     CanvasToCompositorMsg, CompositionPipeline, CompositorMsg, CompositorReceiver,
@@ -21,12 +23,10 @@ use embedder_traits::Cursor;
 use euclid::{Point2D, Rect, Scale, Transform3D, Vector2D};
 use fnv::{FnvHashMap, FnvHashSet};
 use gfx::rendering_context::RenderingContext;
-use gfx_traits::{Epoch, WebRenderEpochToU16};
 use image::{DynamicImage, ImageFormat};
 use ipc_channel::ipc;
 use libc::c_void;
 use log::{debug, error, info, trace, warn};
-use msg::constellation_msg::{PipelineId, TopLevelBrowsingContextId, WebViewId};
 use net_traits::image::base::Image;
 use net_traits::image_cache::CorsStatus;
 use pixels::PixelFormat;

components/compositing/webview.rs

@@ -4,7 +4,7 @@
 
 use std::collections::HashMap;
 
-use msg::constellation_msg::{PipelineId, WebViewId};
+use base::id::{PipelineId, WebViewId};
 use webrender_api::units::DeviceRect;
 
 #[derive(Debug, Default)]
@@ -113,7 +113,7 @@ impl<WebView> WebViewManager<WebView> {
 mod test {
     use std::num::NonZeroU32;
 
-    use msg::constellation_msg::{
+    use base::id::{
         BrowsingContextId, BrowsingContextIndex, PipelineNamespace, PipelineNamespaceId,
         TopLevelBrowsingContextId,
     };

components/compositing/windowing.rs

@@ -7,14 +7,15 @@
 use std::fmt::{Debug, Error, Formatter};
 use std::time::Duration;
 
+use base::id::{PipelineId, TopLevelBrowsingContextId};
 use embedder_traits::{EmbedderProxy, EventLoopWaker};
 use euclid::Scale;
 use gfx::rendering_context::RenderingContext;
 use keyboard_types::KeyboardEvent;
 use libc::c_void;
-use msg::constellation_msg::{PipelineId, TopLevelBrowsingContextId, TraversalDirection};
 use script_traits::{
-    GamepadEvent, MediaSessionActionType, MouseButton, TouchEventType, TouchId, WheelDelta,
+    GamepadEvent, MediaSessionActionType, MouseButton, TouchEventType, TouchId, TraversalDirection,
+    WheelDelta,
 };
 use servo_geometry::DeviceIndependentPixel;
 use servo_url::ServoUrl;