src,lib: rename FSReqWrap to FSReqCallback
Given that FSReqPromise does not inherit from FSReqWrap, FSReqWrap should be renamed FSReqCallback to better describe what it does.
First of a few upcoming fs
refactorings :)
Checklist
-
make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
tests and/or benchmarks are included -
documentation is changed or added -
commit message follows commit guidelines