Introduce setDefaultCharset() in AbstractResourceBasedMessageSource #36413
Description
Currently, AbstractResourceBasedMessageSource has a setDefaultEncoding() method which accepts the name of the default encoding character set.
Although we have recently made a concerted effort to introduce support for supplying a Charset instead of a character set's name, we overlooked this particular scenario.
In light of that, we should introduce setDefaultCharset(Charset) and Charset getDefaultCharset() methods in AbstractResourceBasedMessageSource and make direct use of the Charset wherever feasible.