Restructure spring-boot-test packages

Create a new package structure for `spring-boot-test` and deprecate
existing classes.

Fixes gh-5293

spring-boot-test/src/test/resources/org/springframework/boot/test/context/SpringApplicationConfigurationGroovyConventionConfigurationTestsContext.groovy

@@ -0,0 +1,3 @@
+beans {
+	foo String, "World"
+}

spring-boot-test/src/test/resources/org/springframework/boot/test/context/SpringApplicationConfigurationXmlConventionConfigurationTests-context.xml

@@ -0,0 +1,13 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<beans xmlns="http://www.springframework.org/schema/beans"
+	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context"
+	xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
+				http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd">
+
+	<bean id="foo" class="java.lang.String">
+		<constructor-arg>
+			<value>World</value>
+		</constructor-arg>
+	</bean>
+
+</beans>