Fix errors/html/error_exception.php

[kenjis]

Description
errors/html/error_exception.php throws error when constants contain resource and can't see the real exception.

ErrorException #1

Uncaught ErrorException: htmlspecialchars() expects parameter 1 to be string, resource given in .../app/Views/errors/html/error_exception.php:182 Stack trace: #0 [internal function]: CodeIgniter\Debug\Exceptions->errorHandler(2, 'htmlspecialchar...', '/Users/kenji/wo...', 182, Array) #1 .../app/Views/errors/html/error_exception.php(182): htmlspecialchars(Resource id #4, 8, 'UTF-8') #2 .../vendor/codeigniter4/codeigniter4/system/Debug/Exceptions.php(281): include('/Users/kenji/wo...') #3 .../vendor/codeigniter4/codeigniter4/system/Debug/Exceptions.php(147): CodeIgniter\Debug\Exceptions->render(Object(...\Exception\NotSupportedException), 500) #4 [internal function]: CodeIgniter\Debug\Exceptions->exceptionHandler(Object(...\Exception\NotSupportedException)) #5 {main} thrown 

Checklist:

• Securely signed commits
• Component(s) with PHPdocs
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide

[kenjis]

@samsonasik @paulbalandan
Fixed:

• use is_string($value) in all places
• add </pre>
• escape print_r() output

[samsonasik]

@kenjis thank you for the PR.
@paulbalandan thank you for the review.