Replace calling FormState::setErrorByName() with an empty string with a new method

It took me a while to find that calling setErrorByName() was the way to set an error not by name. At least the parameter documentation should describe this.

Akhil Babu → made their first commit to this issue’s fork.

The FormState::setErrorByName() function accepts 2 arguments, $name and $message. When $name is provided, the corresponding element will be highlighted during validation errors. If $name is empty or '', the error message will still be displayed above the form, but no form elements will be highlighted.

From the issue description, I assume that calling setErrorByName() with an empty $name parameter (Like $form_state->setErrorMessage('', 'Custom error message')) should be deprecated. Based on this, I have created a new function setErrorMessage() that will be called when $name is empty as a first step.