Fix all PHP 8.1 test failures

* `strftime()` has been replaced with a polyfill based on `DateTime`.
* Explicit type casts/assertions added where required by PHP 8.1
* `filter_var(…, FILTER_SANITIZE_STRING)` replaced with `strip_tags()`
  or HTML entity encoding of quotation marks, depending on a guess of
  what the intended "sanitization" was
* `http_build_query()` usage type mismatches fixed
* Removed usages of the `FILE_TEXT` constant
* To avoid breaking PHP 5.6 compatibility (function return types),
  `e_session_db` no longer implements `SessionHandlerInterface`.
  Instead, the alternative non-OOP invocation of
  `session_set_save_handler()` is used instead to apply the session
  handler.
* The shim for `strptime()` still calls the native function if available
  but now suppresses the deprecation warning.

* `e_db_pdo` explicitly asks for `PDO::ATTR_STRINGIFY_FETCHES` to
  maintain consistent behavior with past versions of PHP.
* `e_db_mysql` explicitly sets `mysqli_report(MYSQLI_REPORT_OFF)` to
  maintain consistent behavior with past versions of PHP.

* Removed pointless random number generator seed from `banner` plugin
* Workaround for `COUNT(*)` SQL query in
  `validatorClass::dbValidateArray()` without a proper API for avoiding
  SQL injection

e107_admin/admin_log.php

@@ -371,7 +371,7 @@ class admin_log_ui extends e_admin_ui
 			if(($action == "backdel") && isset($_POST['backdeltype']))
 			{
 			//	$old_date = intval($qs[1]);
-				$old_string = strftime("%d %B %Y", $old_date);
+				$old_string = e_date::strftime("%d %B %Y", $old_date);
 				$qry = "dblog_datestamp < ".$old_date; // Same field for both logs
 
 				switch($_POST['backdeltype'])