On the Advanced Search page for Maniphest at /maniphest/query/advanced/, the "Page Size" field is empty.
Thus it does not expose that by default Maniphest queries via the web UI are limited to only 100 results - 100 is the "limit" value defined in the parent class src/applications/search/engine/PhabricatorApplicationSearchEngine.php via getPageSize().
This leads to users confused about missing results.
Historically, the 100 value for the "Page Size" in ManiphestTaskSearchEngine.php was introduced in rPa82c3a89144eba7c41ade2b1db01260cd92273f0 (and at that time exposed in the UI) and removed in rPb8b4279a8ad2351a9d8ae5367ba2b4174cb3d1d1#change-DofiWYgC7zEt when introducing SearchField classes.
Thus introduce a setDefaultValue() function for SearchFields.
Then make the "Page Size" field definition in the Maniphest Query UI use it to set 100.
This change does not affect the Conduit API because setPagerLimitForConduit() in src/applications/search/engine/PhabricatorApplicationSearchEngine.php remains unchanged.
Closes T15676