Allow negative line width for :box face attribute

Allow negative line width for :box face attribute

Separate values for box line width and height and allow both to be
negative which makes the visual width and height of the boxed string
unchanged (Bug#13011).

* doc/lispref/display.texi (Face Attributes): Modify :box attribute
description to reflect the new possibilities.
* lisp/cus-face.el (custom-face-attributes): Set box attribute to get
two integer to set vertical and horizontal width and modify pre-filter
to accept dotted list of two int as valid box attribute.
* src/dispextern.h (face): Use two int for box horizontal and vertical
line width.

* src/nsfont.m (nsfont_draw): Use new face attributes.
* src/nsterm.m (ns_draw_box, ns_draw_relief): Support separated
horizontal and vertical box line width.
(ns_dumpglyphs_box_or_relief, ns_maybe_dumpglyphs_background)
(ns_dumpglyphs_image, ns_draw_glyph_string_foreground)
(ns_draw_composite_glyph_string_foreground): Use new face attributes.

* src/w32term.c (w32_draw_box_rect, w32_draw_relief_rect): Support
separated horizontal and vertical box line width.
(x_draw_glyph_string_background, x_draw_glyph_string_foreground)
(x_draw_composite_glyph_string_foreground)
(x_draw_glyphless_glyph_string_foreground, x_draw_glyph_string_box)
(x_draw_image_foreground, x_draw_image_relief)
(w32_draw_image_foreground_1, x_draw_image_glyph_string): Use new face
attributes.

* src/xfaces.c (Sinternal_set_lisp_face_attribute, realize_x_face):
Accept box attribute as a list of two ints.

* src/xdisp.c (estimate_mode_line_height, produce_image_glyph)
(produce_xwidget_glyph, x_produce_glyphs): Use new face attributes.
* src/xterm.c (x_draw_box_rect, x_draw_relief_rect): Support separated
horizontal and vertical box line width.
(x_draw_glyph_string_background, x_draw_glyph_string_foreground)
(x_draw_composite_glyph_string_foreground)
(x_draw_glyphless_glyph_string_foreground, x_draw_glyph_string_box)
(x_draw_image_foreground, x_draw_image_relief, x_draw_image_foreground_1)
(x_draw_image_glyph_string): Use new face attributes.