Move Stylo to its own repo (#31350)

* Remove packages that were moved to external repo

* Add workspace dependencies pointing to 2023-06-14 branch

* Fix servo-tidy.toml errors

* Update commit to include #31346

* Update commit to include servo/stylo#2

* Move css-properties.json lookup to target/doc/stylo

* Remove dependency on vendored mako in favour of pypi dependency

This also removes etc/ci/generate_workflow.py, which has been unused
since at least 9e71bd6a70.

* Add temporary code to debug Windows test failures

* Fix failures on Windows due to custom target dir

* Update commit to include servo/stylo#3

* Fix license in tests/unit/style/build.rs

* Document how to build with local Stylo in Cargo.toml

tests/unit/style/build.rs

@@ -0,0 +1,8 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+fn main() {
+    // Dummy build script, just so the code can get env!("OUT_DIR").
+    println!("cargo:rerun-if-changed=build.rs");
+}