Include ALL source artifacts in published sources jars

This commit updates the Gradle build to ensure that *all* source
artifacts are including in published 'sources' jars.

To achieve this, we are now assembling 'sources' jars from
'sourceSets.main.allSource' and not explicitly including or excluding
anything by default.

Issue: SPR-12085
(cherry picked from commit 07629a3c7c)

build.gradle

@@ -156,10 +156,10 @@ configure(subprojects - project(":spring-build-src")) { subproject ->
 		logging.captureStandardOutput LogLevel.INFO // suppress "## warnings" message
 	}
 
-	task sourcesJar(type: Jar, dependsOn:classes) {
-		classifier = "sources"
-		from sourceSets.main.allJava.srcDirs
-		include "**/*.java", "**/*.aj"
+	task sourcesJar(type: Jar, dependsOn: classes) {
+		classifier = 'sources'
+		from sourceSets.main.allSource
+		// don't include or exclude anything explicitly by default. See SPR-12085.
 	}
 
 	task javadocJar(type: Jar) {