AsString indy logic does not handle refinements

[headius]

The logic for AsString, in AsStringInvokeSite, only supports non-refined invocation of the to_s method. When refinements are active, it falls back on normal invocation.

However, we also modified the IRBuilder such that it only uses AsString when refinements are active, since otherwise we can use faster logic for coercing dynamic string elements to Strings.

The result of this is that the indy AsString site is not currently being used. I discovered this while attempting to increase the code coverage of indy JIT.

Either this class should be deleted, or it should be improved to support refined invocation. No other indy logic currently supports fast refined invocation, so this is part of a larger project to add that capability.