Relocate shaded JSON API in annotation-processor

Move the 'shade' copy of the JSON API to a separate src folder to make
it clearer that we don't own the code. Also polished some formatting
and suppressed a few warnings.

Closes gh-10307

spring-boot-tools/spring-boot-configuration-processor/pom.xml

@@ -40,6 +40,24 @@
 					<proc>none</proc>
 				</configuration>
 			</plugin>
+			<plugin>
+				<groupId>org.codehaus.mojo</groupId>
+				<artifactId>build-helper-maven-plugin</artifactId>
+				<executions>
+					<execution>
+						<id>add-json-shade-source</id>
+						<phase>generate-sources</phase>
+						<goals>
+							<goal>add-source</goal>
+						</goals>
+						<configuration>
+							<sources>
+								<source>${basedir}/src/json-shade/java</source>
+							</sources>
+						</configuration>
+					</execution>
+				</executions>
+			</plugin>
 		</plugins>
 	</build>
 </project>