better representation for language standards

Currently they're listed as a feature, and can include a limited subset of the language standards (they have c99 and gnu, which is annoying, It would be much nicer to specify "gn99"), but there are some limits to this format (that we've run into in meson). There are some projects (glib in particular) that can be built with gnu99 or c99, but you get more goodies if you use gnu99, so that's preferred, but c99 is acceptable. There currently isn't any way to specify that.

This also ties into the non-c languages, as rust has the concept of "editions", which are basically standards, but with no backwards compatibility guarantees.

Start by reviewing the current representation of language standards in the CPS specification and how it is consumed for Meson projects. Compare the glib case, where gnu99 is preferred but c99 is acceptable, with Rust editions. Done should define a representation that supports preferred and acceptable standards across C and non-C languages.

Written by the indexing model from the issue text.