Handle form and query parameters separately

Previously, form and query parameters were handled together as
request parameters. Howeer, request parameters are a server-side
construct that's specific to the servlet specification. As such
they're not appropriate for the client-side documentation that
Spring REST Docs aims to produce.

This commit replaces support for documenting request parameters
with support for documenting query paramters found in the query
string of the request's URI and for documenting form parameters
found in the form URL encoded body of the request.

Closes gh-832

docs/src/test/java/com/example/mockmvc/FormParameters.java

@@ -0,0 +1,40 @@
+/*
+ * Copyright 2014-2021 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.example.mockmvc;
+
+import org.springframework.test.web.servlet.MockMvc;
+
+import static org.springframework.restdocs.mockmvc.MockMvcRestDocumentation.document;
+import static org.springframework.restdocs.request.RequestDocumentation.formParameters;
+import static org.springframework.restdocs.request.RequestDocumentation.parameterWithName;
+import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.post;
+import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;
+
+public class FormParameters {
+
+	private MockMvc mockMvc;
+
+	public void postFormDataSnippet() throws Exception {
+		// tag::form-parameters[]
+		this.mockMvc.perform(post("/users").param("username", "Tester")) // <1>
+				.andExpect(status().isCreated()).andDo(document("create-user", formParameters(// <2>
+						parameterWithName("username").description("The user's username") // <3>
+				)));
+		// end::form-parameters[]
+	}
+
+}