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, 2 insertions, 1 deletions

diff --git a/ports/servoshell/webview.rs b/ports/servoshell/webview.rs
index bbacdb1337d..87795f7a550 100644
--- a/ports/servoshell/webview.rs
+++ b/ports/servoshell/webview.rs
@@ -15,14 +15,15 @@ use euclid::{Point2D, Vector2D};
 use gilrs::{EventType, Gilrs};
 use keyboard_types::{Key, KeyboardEvent, Modifiers, ShortcutMatcher};
 use log::{debug, error, info, trace, warn};
+use servo::base::id::TopLevelBrowsingContextId as WebViewId;
 use servo::compositing::windowing::{EmbedderEvent, WebRenderDebugOption};
 use servo::embedder_traits::{
     CompositorEventVariant, ContextMenuResult, EmbedderMsg, FilterPattern, PermissionPrompt,
     PermissionRequest, PromptDefinition, PromptOrigin, PromptResult,
 };
-use servo::msg::constellation_msg::{TopLevelBrowsingContextId as WebViewId, TraversalDirection};
 use servo::script_traits::{
     GamepadEvent, GamepadIndex, GamepadInputBounds, GamepadUpdateType, TouchEventType,
+    TraversalDirection,
 };
 use servo::servo_config::opts;
 use servo::servo_url::ServoUrl;