Replace very_good_analysis with leancode_lint

[bartekpacia]

This PR does first 50% of #1211, that is: replace very_good_analysis with leancode_lint and fix all warnings that arose (~90 - not so bad, I fixed them all).

The last 50% (integration of custom_lint + fixing warnings that will be triggered) I plan to do in a follow-up PR to make review easier. But if you prefer to have it in a single PR, then that's cool as well.

Review checklist

• [x] Terms and conditions reflect the current change
• [x] Contains enough appropriate tests
• [ ] If aimed at production, writes a new summary in whatsnew/whatsnew-pt-PT
• [ ] Properly adds an entry in changelog.md with the change
• [ ] If PR includes UI updates/additions, its description has screenshots
• [x] Behavior is as expected
• [x] Clean, well-structured code

[codecov[bot]]

Codecov Report

Merging #1212 (663e761) into develop (45fbe04) will increase coverage by 1%. Report is 1 commits behind head on develop. The diff coverage is 15%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #1212 +/- ## ======================================= + Coverage 17% 17% +1% ======================================= Files 229 229 Lines 6975 6982 +7 ======================================= + Hits 1144 1152 +8 + Misses 5831 5830 -1 ```