Create Phan / PHPSTAN extension to replace occ app:check-code

[patrickjahns]

The code-checker inside ownCloud has been useful in the past. Instead of however needing to maintain (and ship it as supportable code), lets move the functionality to a static code analyzer like phan or phpstan

Code in question:
https://github.com/owncloud/core/tree/master/lib/private/App/CodeChecker

cc @PVince81 @DeepDiver1975

[PVince81]

I seem to remember a discussion where it was said that we could extend Phan with rules that would help check that apps are using only OCP symbols and no OC_ ones ?

[patrickjahns]

That is exactly what this ticket is about ;-). Backlog item to remember to do this