Add support for paths to svg.el

Add support for paths to svg.el

* doc/lispref/display.texi (SVG Images): Document svg-path,
svg-clip-path and svg-node (bug#32359).

* doc/lispref/display.texi (SVG Path Commands): New node.

* lisp/svg.el (svg--plist-delete, svg--path-command-symbol)
(svg--elliptical-arc-coordinates, svg--elliptical-arc-command)
(svg--moveto-command, svg--closepath-command)
(svg--lineto-command, svg--horizontal-lineto-command)
(svg--vertical-lineto-command, svg--curveto-command)
(svg--smooth-curveto-command)
(svg--quadratic-bezier-curveto-command)
(svg--smooth-quadratic-bezier-curveto-command)
(svg--eval-path-command, svg-path, svg-clip-path, svg-node): New
functions.