Introduce ToRefType which takes a string value and returns a reference type
or throws an error. Make ToRefType recognize both anyfunc and funcref as
names for the general function, since we've already shipped code that
Make ToValType use ToRefType instead of doing its own parsing.
Make WasmTableObject::construct use ToRefType instead of doing its
own parsing. This is an attempt to have the system do the same
thing everywhere instead of having ad-hoc solutions.
Introduce a ToJSAPIString that will produce "anyfunc" for funcref,
and use that where it's appropriate.
Make the test case converter generate anyfunc instead of funcref.
Change all test cases that use funcref to use anyfunc, in the JS API.