Allow glyphless-char-display to distinguish between X and text terminals.

Allow glyphless-char-display to distinguish between X and text terminals.
Use this for Tabulated List mode.

* lisp/emacs-lisp/tabulated-list.el (tabulated-list-mode): Use a custom
glyphless-char-display table.
(tabulated-list-glyphless-char-display): New var.

* src/term.c (produce_glyphless_glyph): Handle cons cell entry in
glyphless-char-display.

* src/xdisp.c (lookup_glyphless_char_display)
(produce_glyphless_glyph): Handle cons cell entry in
glyphless-char-display.
(Vglyphless_char_display): Document it.