Rename script_layout_interface to layout_api (#37591)

Now that we are standardizing on the `_traits` crates becoming `_api`
and exposing the API of the crate that they get their name from [^1],
`script_layout_interface` becomes `layout_api` as it exposes the API for
`layout` that is used by `script` This brings the crate in line with the
naming of the other ones in `shared`.

[^1]:
https://servo.zulipchat.com/#narrow/channel/263398-general/topic/Organizing.20*_traits.20crates/with/396893711

Testing: This should not change any behavior and thus is covered by
existing tests.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>

python/servo/testing_commands.py

@@ -185,12 +185,12 @@ class MachCommands(CommandBase):
             "fonts",
             "hyper_serde",
             "layout",
+            "layout_api",
             "libservo",
             "metrics",
             "net",
             "net_traits",
             "pixels",
-            "script_layout_interface",
             "script_traits",
             "selectors",
             "servo_config",