Summary:
Passing null as input strings to `substr()` and `preg_match()` is deprecated in PHP 8.
Thus do not call `substr()` when input is `null` and pass an empty string instead of `null` to `preg_match()`. (Not calling `preg_match()` at all here would lead to `Exception: Lexical error on line 1. Unrecognized text. ^`).
Closes T15346
Test Plan: After applying these three changes and following the steps in T15346, tab on the dashboard displays "This tab panel does not have any tabs yet." as expected instead of the previous RuntimeException.
Reviewers: O1 Blessed Committers, valerio.bozzolan
Reviewed By: O1 Blessed Committers, valerio.bozzolan
Subscribers: speck, tobiaswiese, valerio.bozzolan, Matthew, Cigaryno
Maniphest Tasks: T15346
Differential Revision: https://we.phorge.it/D25250
Summary: Ref T13395. Moves all remaining code in "libphutil/" into "arcanist/".
Test Plan: Ran various arc workflows, although this probably has some remaining rough edges.
Maniphest Tasks: T13395
Differential Revision: https://secure.phabricator.com/D20980
