Treat piped item types as alternatives instead of one invalid id

[JeroenDeDauw]

haswbfacet:P1=Q1|Q2 on the item type property was handed to ItemId whole, which rejected it, leaving the
query with no item type: the search applied no type filter, the sidebar showed no facets, and
action=wbfacetsearch failed with wbfs-item-type-required. | already means OR in a facet value filter, and
repeated item type tokens already union, so the value is now split on |, valid ids added and invalid segments
skipped as a single invalid id already was. Piped and repeated forms now select the same items and the same
facets, which remain those of the first item type in the expression.

_{AI-authored — Claude Code, Opus 5 (max); one-line ask from @JeroenDeDauw covering three review findings, one
PR each; no redirections; diff not yet human-reviewed; regression tests seen failing then passing, full extension
PHPUnit suite, phpcs and phpstan clean, and both the search page and the API re-checked on a dev wiki.}

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 76.44%. Comparing base (f41af94) to head (6dbdcff).

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #289      +/-   ##
============================================
+ Coverage     75.51%   76.44%   +0.92%     
- Complexity      429      431       +2     
============================================
  Files            50       50              
  Lines          1401     1405       +4     
============================================
+ Hits           1058     1074      +16     
+ Misses          343      331      -12     

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