Among other things, this removed mention of MediaWiki classes from the
library and adds a README.md that attempts to define constraints for
interoperability between libraries producing MessageValues and formatter
implementations that are expected to handle them.
This also renames "TextParam" to "ScalarParam", as that seems a more
accurate name for the class.
Change-Id: I264dd4de394d734a87929cf4740779e7b7d0e04a
An injectable service interface for message formatting, somewhat
narrowed compared to Message.
Only the text format is implemented in this framework so far, with
getTextFormatter() returning a formatter that converts to the text
format. Other formatters could be added to MessageFormatterFactory.
Bug: T226598
Change-Id: Id053074c1dbcb692e8309fdca602f94a385bca0c
