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/components/script/Cargo.toml b/components/script/Cargo.toml
index 1fc2f1a69cc..45926d07f40 100644
--- a/components/script/Cargo.toml
+++ b/components/script/Cargo.toml
@@ -31,7 +31,9 @@ accountable-refcell = { workspace = true, optional = true }
 app_units = { workspace = true }
 arrayvec = { workspace = true }
 atomic_refcell = { workspace = true }
+background_hang_monitor_api = { workspace = true }
 backtrace = { workspace = true }
+base = { workspace = true }
 base64 = { workspace = true }
 bitflags = { workspace = true }
 bluetooth_traits = { workspace = true }
@@ -74,7 +76,6 @@ media = { path = "../media" }
 metrics = { path = "../metrics" }
 mime = { workspace = true }
 mime_guess = { workspace = true }
-msg = { workspace = true }
 net_traits = { workspace = true }
 num_cpus = { workspace = true }
 num-traits = { workspace = true }