=doc #18657 Doc host and path directives

* also including docs of RequestVals.matchAndExtractHost
  and RequestVals.matchAndExtractHost
* and add Host.create factory methods
* add missing HttpRequest PATCH and OPTIONS
* change to val in matchAndExtractHost for
  fail fast exception

akka-docs-dev/rst/java/http/routing-dsl/directives/method-directives/post.rst

@@ -0,0 +1,17 @@
+.. _-post-java-:
+
+post
+====
+
+Matches requests with HTTP method ``POST``.
+
+This directive filters the incoming request by its HTTP method. Only requests with
+method ``POST`` are passed on to the inner route. All others are rejected with a
+``MethodRejection``, which is translated into a ``405 Method Not Allowed`` response
+by the default ``RejectionHandler``.
+
+
+Example
+-------
+
+.. includecode:: ../../../../code/docs/http/javadsl/server/directives/MethodDirectivesExamplesTest.java#post