ExcludedFiles::isExcluded is expensive for deep paths

[TheOneRing]

We check for all parent folders whether they are hidden.
For deep structures with many files, this is super expensive.

This is called again after a sync for every single file

desktop/src/libsync/syncfilestatustracker.cpp

Line 120 in f9703a3

if (_syncEngine->isExcluded(absolutePath)) {

[Mayurifag]

I might be affected with this problem, because I see files checking for sync too much:

That is triggered every several seconds (10-15?) and since its not 1ms operation but also for several seconds, its kinda visually annoying and makes me think something is wrong.

I have 50gb/16k files with following custom regexps for exclude (not sure if they are optimal):

So I might use several non optimized for that usage portable software which might cache some files or just touch files without changes without any reason. And that triggers opencloud desktop probably too much.