UseJava: Move helper scripts to subdirectory

Also, exclude them from the help module index.

Modules/UseJava/ClassFilelist.cmake

@@ -0,0 +1,40 @@
+# Distributed under the OSI-approved BSD 3-Clause License.  See accompanying
+# file Copyright.txt or https://cmake.org/licensing for details.
+
+# This script creates a list of compiled Java class files to be added to
+# a jar file.  This avoids including cmake files which get created in
+# the binary directory.
+
+if (CMAKE_JAVA_CLASS_OUTPUT_PATH)
+    if (EXISTS "${CMAKE_JAVA_CLASS_OUTPUT_PATH}")
+
+        set(_JAVA_GLOBBED_FILES)
+        if (CMAKE_JAR_CLASSES_PREFIX)
+            foreach(JAR_CLASS_PREFIX ${CMAKE_JAR_CLASSES_PREFIX})
+                message(STATUS "JAR_CLASS_PREFIX: ${JAR_CLASS_PREFIX}")
+
+                file(GLOB_RECURSE _JAVA_GLOBBED_TMP_FILES "${CMAKE_JAVA_CLASS_OUTPUT_PATH}/${JAR_CLASS_PREFIX}/*.class")
+                if (_JAVA_GLOBBED_TMP_FILES)
+                    list(APPEND _JAVA_GLOBBED_FILES ${_JAVA_GLOBBED_TMP_FILES})
+                endif ()
+            endforeach()
+        else()
+            file(GLOB_RECURSE _JAVA_GLOBBED_FILES "${CMAKE_JAVA_CLASS_OUTPUT_PATH}/*.class")
+        endif ()
+
+        set(_JAVA_CLASS_FILES)
+        # file(GLOB_RECURSE foo RELATIVE) is broken so we need this.
+        foreach(_JAVA_GLOBBED_FILE ${_JAVA_GLOBBED_FILES})
+            file(RELATIVE_PATH _JAVA_CLASS_FILE ${CMAKE_JAVA_CLASS_OUTPUT_PATH} ${_JAVA_GLOBBED_FILE})
+            set(_JAVA_CLASS_FILES ${_JAVA_CLASS_FILES}${_JAVA_CLASS_FILE}\n)
+        endforeach()
+
+        # write to file
+        file(WRITE ${CMAKE_JAVA_CLASS_OUTPUT_PATH}/java_class_filelist ${_JAVA_CLASS_FILES})
+
+    else ()
+        message(SEND_ERROR "FATAL: Java class output path doesn't exist")
+    endif ()
+else ()
+    message(SEND_ERROR "FATAL: Can't find CMAKE_JAVA_CLASS_OUTPUT_PATH")
+endif ()