(cherry picked from commit dc6e2f79)

It's used in a single module so it makes no sense to define it as project-level library.

in "AtomicFieldUpdater issues" inspection

IDEA-182696

completion results should not be cached even if called after resolved conflicts

PSI structure can be unexpectedly inconsistent at that moment

otherwise property tests report stub/AST mismatch sometimes on very invalid code

because: it's shorter,
and it doesn't leak Windows handles due to unclosed Files.list stream
(which leads to Groovy compiler tests blinking on Windows)

Also get rid of duplication