Add PHP v8.1 Compatibility

[dleffler]

There are some breaking changes in PHP v8.1 (8.1.0alpha2)

• substr(): Passing null to parameter 1 ($string) of type string is deprecated
• mysqli_real_escape_string(): Passing null to parameter 2 ($string) of type string is deprecated
• preg_replace(): Passing null to parameter 3 ($subject) of type array|string is deprecated
• preg_split(): Passing null to parameter 3 ($limit) of type int is deprecated
• preg_replace_callback(): Passing null to parameter 3 ($subject) of type array|string is deprecated
• Uncaught mysqli_sql_exception: You have an error in your SQL syntax

[dleffler]

In the next patch (v2.6.0patch2) we've added some code which should prevent the fatal errors (mostly in the mysqli module), though the warnings listed above have not yet been addressed.

[dleffler]

Also strftime() is deprecated and must be replaced by date(). This also requires changing the 'format' strings, however we'll insert a function to change the format strings, at least initially.

[dleffler]

It should be noted that several 3rd party libraries are not yet PHP 8.1 compliant

• SCSSPHP (v1.6.0)
• Smarty (v3.1.39)

[dleffler]

Fixed with v2.6.0patch2