RFR: 8265123: Add static factory methods to com.sun.net.httpserver.Filter

[Julia Boes]

On Tue, 13 Apr 2021 15:39:17 GMT, Julia Boes <jboes at openjdk.org> wrote:

> Add two static factory methods to com.sun.net.httpserver.Filter that facilitate the creation of pre- and post-processing Filters: 
> 
> `public static Filter beforeResponse(String description, Consumer<HttpExchange> filterImpl) {}`
> `public static Filter afterResponse(String description, Consumer<HttpExchange> filterImpl) {}`

Updated the method names and specifications, which now include @apiNotes and examples. I'm not sure if we want to keep both examples for `afterHandler`? 
Added a test for the uncommon case where the filters handle the exchange (not the handler).

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PR: https://git.openjdk.java.net/jdk/pull/3468