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_handlers/upload_handler.php

@@ -195,7 +195,7 @@ function process_uploaded_files($uploaddir, $fileinfo = FALSE, $options = NULL)
 	
 	foreach ($files['name'] as $key=>$name)
 	{
-		$name = filter_var($name, FILTER_SANITIZE_STRING);
+		$name = $tp->filter($name, 'str');
 
 		$first_error = FALSE; // Clear error flag
 		if (($name != '') || $files['size'][$key]) // Need this check for things like file manager which allow multiple possible uploads