Auto merge of #12295 - jimberlage:12158/shell-linting, r=aneeshusa

Add linting for shell scripts

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This changes tidy to check shell scripts for the proper shebang and
options.  It does not check that variables are formatted correctly.  It
also adds a check for the MPL 2.0 license in shell scripts.

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix #12158 (github issue number if applicable).

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- [X] There are tests for these changes OR
- [ ] These changes do not require tests because _____

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python/tidy/servo_tidy_tests/test_tidy.py

@@ -48,6 +48,12 @@ class CheckTidiness(unittest.TestCase):
         self.assertEqual('incorrect license', errors.next()[2])
         self.assertNoMoreErrors(errors)
 
+    def test_shell(self):
+        errors = tidy.collect_errors_for_files(iterFile('shell_tidy.sh'), [], [tidy.check_shell], print_text=False)
+        self.assertEqual('script does not have shebang "#!/usr/bin/env bash"', errors.next()[2])
+        self.assertEqual('script is missing options "set -o errexit", "set -o pipefail"', errors.next()[2])
+        self.assertNoMoreErrors(errors)
+
     def test_rust(self):
         errors = tidy.collect_errors_for_files(iterFile('rust_tidy.rs'), [], [tidy.check_rust], print_text=False)
         self.assertEqual('use statement spans multiple lines', errors.next()[2])