servo: Merge #12877 - Tidy config file (from UK992:tidy-toml); r=Wafflespeanut

This is wip workaround for https://github.com/servo/servo/issues/10841
Adds ``servo-tidy.toml`` with configs and ignored dirs, files and packages.
This will allow to set custom configuration per repo.
It's an example how could config file looks like.
I want opinion on that, if this is right approaches and how to improve it.

cc @edunham

Source-Repo: https://github.com/servo/servo
Source-Revision: 1c9650cc90090784c63f5af55628ffe6b57c25ed

servo/python/tidy/servo_tidy_tests/servo-tidy.toml

@@ -0,0 +1,13 @@
+key-outside = ""
+
+[configs]
+skip-check-length = false
+skip-check-licenses = false
+wrong-key = false
+
+[wrong]
+wrong-key = true
+
+[ignore]
+files = []
+directories = []

servo/python/tidy/servo_tidy_tests/test_tidy.py

@@ -23,6 +23,13 @@ class CheckTidiness(unittest.TestCase):
         with self.assertRaises(StopIteration):
             errors.next()
 
+    def test_tidy_config(self):
+        errors = tidy.check_config_file(os.path.join(base_path, 'servo-tidy.toml'))
+        self.assertEqual('invalid config key \'key-outside\'', errors.next()[2])
+        self.assertEqual('invalid config key \'wrong-key\'', errors.next()[2])
+        self.assertEqual('invalid config table [wrong]', errors.next()[2])
+        self.assertNoMoreErrors(errors)
+
     def test_spaces_correctnes(self):
         errors = tidy.collect_errors_for_files(iterFile('wrong_space.rs'), [], [tidy.check_by_line], print_text=False)
         self.assertEqual('trailing whitespace', errors.next()[2])