The copyright checker was allowing files with code above the copyright
line in a few places, mainly as a result of IDEs ordering imports
improperly.
This makes the check more robust, and adds a whitelist of valid lines
that may appear before the copyright line.
Adds two test files: "cli/tests/unit_node/process_test.ts" and
"cli/tests/unit_node/child_process_test.ts"
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Co-authored-by: Yoshiya Hinosawa <stibium121@gmail.com>
