CSS Filter: allow clip-path and some related functions.

"clip-path": Used to clip an element via inside of polygon.
https://developer.mozilla.org/en-US/docs/Web/CSS/clip-path

"circle", "ellipse", "line", "polygon", "polyline": Functions used to
create SVG shapes. Same uses as `rect`.
https://developer.mozilla.org/en-US/docs/Web/SVG/Element/polygon

r2/r2/lib/cssfilter.py

@@ -139,6 +139,7 @@
     "caption-side",
     "clear",
     "clip",
+    "clip-path",
     "color",
     "content",
     "counter-increment",
@@ -292,12 +293,15 @@
 SAFE_FUNCTIONS = {
     "attr",
     "calc",
+    "circle",
     "counter",
     "counters",
     "cubic-bezier",
+    "ellipse",
     "hsl",
     "hsla",
     "lang",
+    "line",
     "linear-gradient",
     "matrix",
     "matrix3d",
@@ -307,6 +311,8 @@
     "nth-last-of-type",
     "nth-of-type",
     "perspective",
+    "polygon",
+    "polyline",
     "radial-gradient",
     "rect",
     "repeating-linear-gradient",