[LINTER] Enforce source code file name conventions
Summary:
Follow-up for D3572.
This linter ensures the source file names are compliant with the naming
conventions from the developer notes.
Test Plan:
arc lint --everything # No error
Rename src/addrdb.cpp to src/addrDb.cpp
arc lint -- src/addrDb.cpp
Check the error is catched by the linter.
Reviewers: #bitcoin_abc, deadalnix
Reviewed By: #bitcoin_abc, deadalnix
Differential Revision: https://reviews.bitcoinabc.org/D3593