[stable8] Use transactions when renaming directory contents

[MorrisJobke]

backport of #13948

cc @DeepDiver1975 @icewind1991

[ghost]

Refer to this link for build results (access rights to CI server needed):
https://ci.owncloud.org//job/pull-request-analyser-ng-simple/10261/
Test PASSed.

[PVince81]

Bumped into this weird issue: #14757

Now thinking of it, it could somehow be due to the transaction.

[christianrj]

Some of the bugs I reported related to rename problems:
#10711
#11847
#12659
#12661

@PVince81
Maybe some of them has something to do with #14757

[DeepDiver1975]

Bumped into this weird issue: #14757

Now thinking of it, it could somehow be due to the transaction.

so - we better holds this back for now 👎

[PVince81]

Thing is, @jnfrmarks managed to recreate the same issue (mysql lock) on 8.0.2 with smashbox, so I'm not 100% sure whether what I observed was really due to this change or my general "unluck" of being able to trigger random race conditions.

[MorrisJobke]

@PVince81 We can redo this easiely, but if it really cause an problem, then we better analyse this before a backport and not once it hit users ;)

[PVince81]

So far it seems that the issues we were seeing were not related to this addition, so we might maybe want to reopen/resend this, at least as a quickfix to reduces the probability of data loss here #13391