Inspired by cl/3191 and
https://git.lix.systems/delroth/lix/commit/ae0247cbb4fc739ab013dc87d02e5f3191cf25ab.
`coerceToString` takes now an enumeration that lives in `value.hh`, this
enumeration is meant to represent increasing subsets of behaviors, e.g.
any level above Strict should do what the previous levels do and extra
behavior until `ToString`, which transforms many Nix values into an
arbitrary string representation, e.g. `null` to `""`.
Change-Id: Ief7a4756e8c0660e197623efebeaf07710746ec7
Signed-off-by: Raito Bezarius <raito@lix.systems>
Co-authored-by: Pierre Bourdon <delroth@gmail.com>
