Implement [Inline] interfaces

Inline interfaces just appear as a Rust type and in the TypeId hierarchy.
They are completely invisible on the JS side.

components/script/dom/bindings/codegen/parser/WebIDL.py

@@ -1695,7 +1695,8 @@ class IDLInterface(IDLInterfaceOrNamespace):
                   identifier == "ProbablyShortLivingObject" or
                   identifier == "LegacyUnenumerableNamedProperties" or
                   identifier == "NonOrdinaryGetPrototypeOf" or
-                  identifier == "Abstract"):
+                  identifier == "Abstract" or
+                  identifier == "Inline"):
                 # Known extended attributes that do not take values
                 if not attr.noArguments():
                     raise WebIDLError("[%s] must take no arguments" % identifier,