Overhaul repeatable @TestPropertySource support

Prior to this commit, if multiple, directly present
`@TestPropertySource` annotations declared the same property, the
precedence ordering was top-down instead of bottom-up, in contrast to
the semantics for class hierarchies. In other words, a subsequent
`@TestPropertySource` annotation could not override a property in a
previous `@TestPropertySource` annotation.

This commit overhauls the internals of `TestPropertySourceUtils` in
order to provide proper support for property overrides within local,
directly present `@TestPropertySource` declarations.

Specifically, the `locations` and `properties` attributes from all
`@TestPropertySource` declarations that are directly present or
meta-present on a given class are now merged into a single instance of
`TestPropertySourceAttributes` internally, with assertions in place to
ensure that such "same level" `@TestPropertySource` declarations do not
configure different values for the `inheritLocations` and
`inheritProperties` flags. Effectively, all "same level"
`@TestPropertySource` declarations are treated internally as if there
were only one such annotation declared by the user.

See gh-23320

spring-test/src/test/resources/log4j2-test.xml

@@ -25,6 +25,7 @@
 		<Logger name="org.springframework.test.context.support.DelegatingSmartContextLoader" level="info" />
 		<Logger name="org.springframework.test.context.support.AbstractGenericContextLoader" level="info" />
 		<Logger name="org.springframework.test.context.support.AnnotationConfigContextLoader" level="info" />
+		<Logger name="org.springframework.test.context.support.TestPropertySourceUtils" level="trace" />
 		<Logger name="org.springframework.beans" level="warn" />
 		<Logger name="org.springframework.test.web.servlet.result" level="debug" />
 -->

spring-test/src/test/resources/org/springframework/test/context/env/repeatable/DefaultPropertiesFileDetectionRepeatedTestPropertySourceTests.properties

@@ -0,0 +1 @@
+default.value = default file

spring-test/src/test/resources/org/springframework/test/context/env/repeatable/TestPropertySourceRepeatableWithDefaultPropertiesFileTests.properties

@@ -1 +0,0 @@
-default.value = a value from default properties file

spring-test/src/test/resources/org/springframework/test/context/env/repeatable/first.properties

@@ -1 +1,3 @@
-first = 1111
+alpha = beta
+first = 1111
+second = 1111

spring-test/src/test/resources/org/springframework/test/context/env/repeatable/local.properties

@@ -1 +1 @@
-key = local value
+key1 = local file

spring-test/src/test/resources/org/springframework/test/context/env/repeatable/meta.properties

@@ -1 +1 @@
-meta = a value from file in the meta-annotation
+key2 = meta file

spring-test/src/test/resources/org/springframework/test/context/env/repeatable/second.properties

@@ -1 +1,2 @@
-second = 2222
+alpha = omega
+second = 2222