Add Order Constant for Filters that wrap the HttpServletRequest

[rwinch]

The idea would be that any Filter that wraps the HttpServletRequest would be before this constant. Any Filter that relies on the wrapped HttpServletRequest would be after the constant. This would help in situations like apache/grails-core#9137

[dsyer]

Can we start by making a list of Filters that we know might wrap the request? Spring Security's main filter is one. Also HiddenHttpMethodFilter. There are various filters in Spring (e.g. *RequestLoggingFilter) that we don't use routinely.

Others: char encoding, cors, resource chain.

The ErrorPageFilter wraps the response, does that count? Spring Cloud wraps the request inside Zuul, does that count? Similar question for the multipart support in Spring - it wraps the request, but not in a Filter.

[dsyer]

OK, there's nothing we can do about the downstream components (like DispatcherServlet wrapping a request). All the filters added explicitly by Spring Boot now have order <= FilterRegistrationBean.REQUEST_WRAPPER_FILTER_MAX_ORDER (value 0).