Add tool bar style text-image-horiz (text to the left of the image).

Add tool bar style text-image-horiz (text to the left of the image).

* lisp/cus-start.el (tool-bar-style): Add text-image-horiz.

* src/gtkutil.c (xg_make_tool_item, xg_show_toolbar_item): Handle tool bar
style text_image_horiz.

* src/lisp.h (Qtext_image_horiz): Declare.

* src/xdisp.c (Qtext_image_horiz): Define.
(syms_of_xdisp): Initialize Qtext_image_horiz.  Add text-image-horiz
to ducumentation of tool-bar-style.

* src/xsettings.c (Ftool_bar_get_system_style): Also check for
Qtext_image_horiz.