New servlet request getRemoteScheme() for servlet 6.

The current servlet request getScheme() returns the name of the scheme used to make this request. As I understand, it is the scheme of the original client request (i.e the one before any proxies).

Consider a scenario:

`Client ------(https)-------Proxy-------(http)--------AppServer`

AppServer: request.getScheme() returns (https)

There is not a convenient way to find the scheme of the Proxy request to the AppServer (i.e (http) in this case)

There are several "Remote" APIs, for example getRemoteAddr(), getRemoteHost(), getRemotePort(), so should there also be a getRemoteScheme() to retrieve the last proxy's request scheme that sent to the server?

Start by reviewing the Servlet 6 request API and the existing getScheme(), getRemoteAddr(), getRemoteHost(), and getRemotePort() methods. Clarify the proxy-to-application scheme semantics and the compatibility or specification questions before proposing the API. Done means the behavior and scope are specified clearly enough for implementation and review.

Written by the indexing model from the issue text.