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/layout/table_row.rs b/components/layout/table_row.rs
index 764386d9033..21aee72bba5 100644
--- a/components/layout/table_row.rs
+++ b/components/layout/table_row.rs
@@ -9,8 +9,8 @@ use std::fmt;
 use std::iter::{Enumerate, Peekable};
 
 use app_units::Au;
+use base::print_tree::PrintTree;
 use euclid::default::Point2D;
-use gfx_traits::print_tree::PrintTree;
 use log::{debug, warn};
 use serde::{Serialize, Serializer};
 use style::computed_values::border_collapse::T as BorderCollapse;