Add ui_cargo_toml_metadata test

[smoelius]

This PR adds a test to check the metadata of packages in the ui_cargo directory.

A recent change to Cargo causes it to warn when it finds multiple packages with the same name in a git dependency (the issue is described here).

Many (if not all) Dylint libraries depend upon clippy_utils. As a result of the change, one now sees the following when building a Dylint library:

warning: skipping duplicate package `fail` found at `/home/smoelius/.cargo/git/checkouts/rust-clippy-4b72815e96774b3d/0cb0f76/tests/ui-cargo/module_style/pass_mod`
warning: skipping duplicate package `fail` found at `/home/smoelius/.cargo/git/checkouts/rust-clippy-4b72815e96774b3d/0cb0f76/tests/ui-cargo/module_style/fail_no_mod`
warning: skipping duplicate package `cargo_common_metadata` found at `/home/smoelius/.cargo/git/checkouts/rust-clippy-4b72815e96774b3d/0cb0f76/tests/ui-cargo/cargo_common_metadata/fail_publish_true`
warning: skipping duplicate package `fail-cargo` found at `/home/smoelius/.cargo/git/checkouts/rust-clippy-4b72815e96774b3d/0cb0f76/tests/ui-cargo/cargo_rust_version/pass_cargo`
warning: skipping duplicate package `fail-clippy` found at `/home/smoelius/.cargo/git/checkouts/rust-clippy-4b72815e96774b3d/0cb0f76/tests/ui-cargo/cargo_rust_version/fail_clippy`
warning: skipping duplicate package `fail-both-same` found at `/home/smoelius/.cargo/git/checkouts/rust-clippy-4b72815e96774b3d/0cb0f76/tests/ui-cargo/cargo_rust_version/fail_both_same`
warning: skipping duplicate package `fail-file-attr` found at `/home/smoelius/.cargo/git/checkouts/rust-clippy-4b72815e96774b3d/0cb0f76/tests/ui-cargo/cargo_rust_version/fail_file_attr`

There appear to be two contributing factors:

• Some packages in ui_cargo could have a publish = false added to them.
• Some packages in ui_cargo seem to be inconsistently named.

The new test checks that each package in the ui_cargo directory has a name matching one of its parent directories, and publish = false in its metadata (with a few exceptions).

Note that the packages in cargo_common_metadata require special care because publish is the subject of some of the cargo_common_metadata tests.

Also note that this PR adds walkdir as a dev dependency to the clippy package. However, it was already a dependency of clippy_dev and lintcheck. So hopefully this is acceptable.

Our continued thanks for making clippy_utils available, BTW. :)

r? @flip1995

changelog: none

[flip1995]

Oh wow, the ui_cargo tests were a total mess. Thanks for fixing this and ensuring that it stays this way!

@bors r+

[bors]

📌 Commit 5b3300d has been approved by flip1995

It is now in the queue for this repository.

[bors]

⌛ Testing commit 5b3300d with merge bc903cd...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: flip1995
Pushing bc903cd to master...