Adjust for composer-require-checker check.

[sasezaki]

To avoid conflict, I do PR into master branch

• Added Composer\Audoload\ClassLoader into bin/composer-require-checker-config.json , it is soft dependency symbol.
• DOMElement instead of DomElement - https://php.net/DOMElement
  to avoid composer-require-check reports false-positive,
  just did - find src/ -type f -exec sed -i -e 's/DomElement/DOMElement/g' {} \;

Before

$ composer-require-checker --config-file=$(pwd)/bin/composer-require-checker-config.json
ComposerRequireChecker 3.8.0@537138b833ab0f9ad72b667a72bece2a765e88ab
The following 2 unknown symbols were found:
+-------------------------------+--------------------+
| Unknown Symbol                | Guessed Dependency |
+-------------------------------+--------------------+
| Composer\Autoload\ClassLoader |                    |
| DomElement                    |                    |
+-------------------------------+--------------------+

After

composer-require-checker --config-file=$(pwd)/bin/composer-require-checker-config.json
ComposerRequireChecker 3.8.0@537138b833ab0f9ad72b667a72bece2a765e88ab
There were no unknown symbols found.

• Also composer-require-checker v4 check passed.

[AndrolGenhald]

Can we add this check to composer.json scripts and CI?

[orklah]

Thanks!