Fix strict typing issues in lib/base.php

[MorrisJobke]

In preparation for #7392.

[codecov]

Codecov Report

Merging #7814 into master will decrease coverage by 1.64%.
The diff coverage is 0%.

@@             Coverage Diff              @@
##             master    #7814      +/-   ##
============================================
- Coverage     52.87%   51.23%   -1.65%     
- Complexity    23658    24970    +1312     
============================================
  Files          1449     1607     +158     
  Lines         80454    95008   +14554     
  Branches          0     1376    +1376     
============================================
+ Hits          42541    48674    +6133     
- Misses        37913    46334    +8421

Impacted Files	Coverage Δ	Complexity Δ
lib/base.php	3.09% <0%> (ø)	167 <0> (ø)	⬇️
.../tests/Unit/Collaboration/CommentersSorterTest.php	25.55% <0%> (-66.45%)	6% <0%> (ø)
apps/sharebymail/tests/SettingsTest.php	52.17% <0%> (-47.83%)	3% <0%> (ø)
lib/private/Security/RateLimiting/Limiter.php	55.55% <0%> (-44.45%)	5% <0%> (ø)
settings/Controller/EncryptionController.php	54.71% <0%> (-38.84%)	8% <0%> (ø)
settings/Controller/GroupsController.php	64.61% <0%> (-35.39%)	9% <0%> (ø)
...ps/comments/tests/Unit/AppInfo/ApplicationTest.php	69.56% <0%> (-30.44%)	4% <0%> (ø)
lib/private/AvatarManager.php	71.42% <0%> (-28.58%)	4% <0%> (ø)
apps/user_ldap/lib/Configuration.php	42.02% <0%> (-27.86%)	87% <0%> (ø)
apps/encryption/lib/Command/EnableMasterKey.php	75% <0%> (-25%)	5% <0%> (ø)
... and 348 more