Improve error passing task IDs as URL parameter in invalid format

Summary:
Maniphest expects the values of the ids URL parameter to be integers. Example: http://phorge.localhost/maniphest/?ids=1,2,3,4 to show a list of tasks with those IDs.
When passing monograms instead (T prefix, like T123 instead of 123), a cryptic message Expected a numeric scalar or null for %Ld conversion is shown.

Thus check if $this->taskIDs consists of integers only; if not throw a PhutilSearchQueryCompilerSyntaxException with an explanatory error message.

Closes T15838

Test Plan: Go to http://phorge.localhost/maniphest/?ids=T1,T2,T3,T4 before and after applying the patch.

Reviewers: O1 Blessed Committers, avivey

Reviewed By: O1 Blessed Committers, avivey

Subscribers: avivey, tobiaswiese, valerio.bozzolan, Matthew, Cigaryno

Maniphest Tasks: T15838

Differential Revision: https://we.phorge.it/D25669