Fix fatal (PHP8.X) type issue with abs, and amend dol_eval return type

# Fix fatal (PHP8.X) type issue with abs, and amend dol_eval return type

I got the following message:
`Fatal error: Uncaught TypeError: abs(): Argument #1 ($num) must be of type int|float, string given in D:\mdeweerd\workspace\dolibarr\htdocs\projet\list.php on line 233`

I examined the phan report and there was no mention of this because dol_eval was
said to return mixed.

In order to detect such cases, I amended the dol_eval return type to ensure to find
most of the locations where a cast is needed.

htdocs/core/lib/functions.lib.php

@@ -9925,7 +9925,7 @@ function verifCond($strToEvaluate, $onlysimplestring = '1')
  * @param	string	$onlysimplestring	'0' (deprecated, do not use it anymore)=Accept all chars,
  * 										'1' (most common use)=Accept only simple string with char 'a-z0-9\s^$_+-.*>&|=!?():"\',/@';',
  * 										'2' (used for example for the compute property of extrafields)=Accept also '[]'
- * @return	mixed						Nothing or return result of eval
+ * @return	void|string					Nothing or return result of eval (even if type can be int, it is safer to assume string and find all potential typing issues as abs(dol_eval(...)).
  * @see verifCond()
  * @phan-suppress PhanPluginUnsafeEval
  */