R1:96ae4ba13acb

PHP 8.1: fixes for strlen() not accepting NULL anymore, part 2

Summary:
This is a fix for PHP 8.1 deprecation of strlen(NULL), for these Phorge components:

- scripts
- aphront
- project

The strlen() was used in Phabricator to check if a generic value was a non-empty string.
For this reason, Phorge adopts phutil_nonempty_string() that checks that.

Note: this may highlight other absurd input values that might be worth correcting
instead of just ignoring. If your phutil_nonempty_string() throws an…