Add placeholder functions for save_ascii, save_binary for octave_java (bug #45694). * ov-java.h: (save_ascii, load_ascii, save_binary, load_binary): New function prototypes overriding defaults in ov.h. * ov-java.cc (save_ascii, save_binary): New functions emit warning about inability to save java objects, and then return true so that other variables can be saved. * ov-java.cc (load_ascii, load_binary): New functions silently skip over null octave_java elements in a file produced by save_ascii() or save_binary().

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