[stable10] Filter unavailable users and remove unavailable shares on polling

[phil-davis]

Backport #35010
so that stable10 QA tarball is more up-to-date

Also note, has been backported to release-10.2.0 in PR #35073

[codecov]

Codecov Report

Merging #35106 into stable10 will increase coverage by <.01%.
The diff coverage is 79.31%.

@@              Coverage Diff               @@
##             stable10   #35106      +/-   ##
==============================================
+ Coverage       64.46%   64.47%   +<.01%     
- Complexity      20064    20068       +4     
==============================================
  Files            1286     1286              
  Lines           76928    76950      +22     
  Branches         1307     1307              
==============================================
+ Hits            49594    49611      +17     
- Misses          26953    26958       +5     
  Partials          381      381

Flag	Coverage Δ	Complexity Δ
#javascript	53.01% <ø> (ø)	0 <ø> (ø)	⬇️
#phpunit	65.68% <79.31%> (ø)	20068 <3> (+4)	⬆️

Impacted Files	Coverage Δ	Complexity Δ
...s/federatedfilesharing/lib/AppInfo/Application.php	45.89% <0%> (-0.97%)	19 <0> (ø)
...atedfilesharing/lib/Command/PollIncomingShares.php	98.52% <100%> (+0.41%)	13 <2> (+2)	⬆️
apps/files_sharing/lib/External/Manager.php	77.38% <40%> (-1.28%)	32 <1> (+2)
lib/private/Server.php	86.66% <0%> (+0.11%)	253% <0%> (ø)	⬇️

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[phil-davis]

change was merged from release-10.2.0 branch