Add utilities to help with JSON testing

Add Jackson, Gson and Basic String helper classes that allow AssertJ
assertions to be used to test JSON.

Fixes gh-5471

spring-boot-test/src/test/resources/org/springframework/boot/test/json/different.json

@@ -0,0 +1,6 @@
+{
+   "gnirps":[
+      "boot",
+      "framework"
+   ]
+}

spring-boot-test/src/test/resources/org/springframework/boot/test/json/example.json

@@ -0,0 +1,4 @@
+{
+   "name" : "Spring",
+   "age" : 123
+}

spring-boot-test/src/test/resources/org/springframework/boot/test/json/lenient-same.json

@@ -0,0 +1,6 @@
+{
+   "spring":[
+      "framework",
+      "boot"
+   ]
+}

spring-boot-test/src/test/resources/org/springframework/boot/test/json/simpsons.json

@@ -0,0 +1,19 @@
+{
+   "familyMembers":[
+      {
+         "name":"Homer"
+      },
+      {
+         "name":"Marge"
+      },
+      {
+         "name":"Bart"
+      },
+      {
+         "name":"Lisa"
+      },
+      {
+         "name":"Maggie"
+      }
+   ]
+}

spring-boot-test/src/test/resources/org/springframework/boot/test/json/source.json

@@ -0,0 +1,6 @@
+{
+   "spring":[
+      "boot",
+      "framework"
+   ]
+}

spring-boot-test/src/test/resources/org/springframework/boot/test/json/types.json

@@ -0,0 +1,19 @@
+{
+   "str":"foo",
+   "num":5,
+   "bool":true,
+   "arr":[
+      42
+   ],
+   "colorMap":{
+      "red":"rojo"
+   },
+   "whitespace":"    ",
+   "emptyString":"",
+   "emptyArray":[
+
+   ],
+   "emptyMap":{
+
+   }
+}