Add StreamReadCapability for further format-based/format-agnostic handling improvements

[cowtowncoder]

One common problem when trying to make "challenging" formats like XML or CSV work well with databinding is that of enabling some format-specific deviations: databind is format-agnostic and should not know details of format; but in some cases it would be really nice to have capability-based changes to handling. So far JsonParser has couple of such methods (requiresCustomCodec(), canParseAsync()), but adding more methods does not seem very scalable.

With 2.12 there is need for couple of new capabilities specifically for improved support of XML.
It would make sense to add an enum-based "feature" style accessor: let's call enum StreamReadCapability and add necessary support for accessing set of such features via JsonParser.getReadCapabilities().