[Build] Use JDK in JAVA_HOME to run the Java source scripts

This increases the probability that the same jvm running the maven build
is used to run the java source scripts.
Maven's launch script by default uses the java executable referenced in
$JAVA_HOME/bin first and only then searches the PATH environment
variable.
Using the java exe at JAVA_HOME also simplifies to control which jvm is
actually used. For example when launching a Maven build from the Eclipse
IDE JAVA_HOME is set to the jvm running that build by Eclipse
automatically, but PATH is not modified.

binaries/pom.xml

@@ -120,7 +120,7 @@
 								</goals>
 								<configuration>
 									<target>
-										<exec executable="java" dir="${swtMainProject}" failonerror="true">
+										<exec executable="${java.home}/bin/java" dir="${swtMainProject}" failonerror="true">
 											<arg line="-Dws=${ws} -Darch=${arch} build-scripts/CollectSources.java -javaSources '${project.basedir}/src' "/>
 										</exec>
 									</target>
@@ -139,7 +139,7 @@
 										<if><equals arg1="${native}" arg2="${ws}.${os}.${arch}"/>
 											<then>
 												<property name="build_dir" value="${project.build.directory}/natives-build-temp"/>
-												<exec executable="java" dir="${swtMainProject}" failonerror="true">
+												<exec executable="${java.home}/bin/java" dir="${swtMainProject}" failonerror="true">
 													<arg line="-Dws=${ws} build-scripts/CollectSources.java -nativeSources '${build_dir}'"/>
 												</exec>
 												<property name="SWT_JAVA_HOME" value="${java.home}"/><!-- Not overwritten if already set, e.g. as CLI argument -->