Fix "Map omits required key" exception by comparing result order against modern field keys
Summary:
Sorting a Maniphest search query by custom fields throws a "Map returned omits required key" exception.
The `isCustomFieldOrderKey()` check still tested against legacy field key format (for example `[custom:]std:maniphest:deadline.due`) while the code passes modern field key format (for example `custom.deadline.due`).
After fixing this, `PhutilTypeSpec::checkMap()` throws an exception when a non-optional (extra) key `$column` is in `$columns` but not in the array of type parameters below to check against:
`"Got unexpected parameters: customfield, customfield.index.table, customfield.index.key"`
Thus add optional types for customfields in `buildPagingClauseFromMultipleColumns()` to allow them instead of throwing another exception.
Closes T15631
Test Plan:
* Have a custom field (with search: true) defined via http://phorge.localhost/config/edit/maniphest.custom-field-definitions/
* Have two tasks have the custom field set
* Go to http://phorge.localhost/maniphest/query/ , select the custom field (e.g. "Due Date (Reversed)") in the "Order By" field, and click the "Search" button. Iterate through the results via the "Next" button if needed
Reviewers: O1 Blessed Committers, valerio.bozzolan
Reviewed By: O1 Blessed Committers, valerio.bozzolan
Subscribers: tobiaswiese, valerio.bozzolan, Matthew, Cigaryno
Maniphest Tasks: T15631
Differential Revision: https://we.phorge.it/D25504