Use workspace deps consistently and add version requirement (#43243)

In order to prepare for publishing this PR does the following steps (see
commits):

- Move all `path` dependencies to the workspace Cargo.toml, and
reference that.
- Move all path dependencies in the workspace Cargo.toml into a
dedicated section, to make bumping version numbers easier later.
- Add the version requirement. Note that we currently only version bump
servoshell. There was agreement to version everything with the same
version as servoshell, but that be done in a follow-up. The diff is
already large enough as is.
- Add a tidy lint to catch `path` usages outside the root Cargo.toml. I
switched to [`tomllib`] (which was added to the python stdlib in 3.11),
since the third-party `toml` library failed to parse Cargo.toml files
with `workspace.version` (did not like the `.` in a `key`).


[`tomllib`]: https://docs.python.org/3/library/tomllib.html

Testing: Should be covered by regular CI testing.

---------

Signed-off-by: Jonathan Schwender <schwenderjonathan@gmail.com>

python/tidy/tests/path_dependency/Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "test"
+version = "0.0.1"
+license = "MPL-2.0"
+publish = false
+
+[dependencies]
+test-package = { path = "../crate" }