Prior to this commit, when Web MVC attempted to resolve a constructor
argument for a data class constructor with @ModelAttribute binding,
ModelAttributeMethodProcessor failed to unwrap the array returned by
WebRequest.getParameter(String).
According to the Javadoc for WebRequest.getParameter(String), "a
single-value parameter will be exposed as an array with a single
element."
This commit fixes this issue by extracting the single value from such
an array and using that as the constructor argument (potentially
converted by the WebDataBinder).
Closes gh-25200
9ddab9e69b