Deleted recently added API:
    hb_buffer_set_invisible_codepoint()
    hb_buffer_get_invisible_codepoint()

    hb-shape / hb-view --invisible-codepoint

New API:
    hb_buffer_set_invisible_glyph()
    hb_buffer_get_invisible_glyph()

    hb-shape / hb-view --invisible-glyph

Fixes https://github.com/harfbuzz/harfbuzz/issues/1216