Auto merge of #12878 - Manishearth:clip-path, r=heycam

stylo: Support clip-path

Todo:

 - [x] `set_clip_path` (probably needs a bunch of gecko bindings for running constructors/destructors)
 - [ ] Ensure that I've ordered the coordinates correctly
 - [ ] Check that it works
 - [x] Might want to convert NS_STYLE_FILL_RULE and NS_RADIUS to enum classes

Depends on:

 - https://github.com/servo/rust-bindgen/pull/29
 - https://github.com/Manishearth/gecko-dev/compare/servo:stylo...Manishearth:clip-path

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ports/geckolib/binding_tools/regen.py

@@ -141,7 +141,8 @@ COMPILATION_TARGETS = {
             "nsStyleCoord::Calc", "nsRestyleHint", "ServoElementSnapshot",
             "nsChangeHint", "SheetParsingMode", "nsMainThreadPtrHandle",
             "nsMainThreadPtrHolder", "nscolor", "nsFont", "FontFamilyList",
-            "FontFamilyType", "nsIAtom", "nsStyleContext"
+            "FontFamilyType", "nsIAtom", "nsStyleContext", "StyleClipPath",
+            "StyleBasicShapeType", "StyleBasicShape"
         ],
         "void_types": [
             "nsINode", "nsIDocument", "nsIPrincipal", "nsIURI",