Make parse_identifiers less complex. Pylint was complaining that it had too
many local variables, and it had a point.
* Lift the constants identifier_regex and exclusion_lines to class
constants (renamed to uppercase because they're constants).
* Lift the per-file loop into a new function parse_identifiers_in_file.
No intended behavior change.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
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