feat(tvix/eval): Give names to builtin arguments

Refactor the arguments of a Builtin to be a vec of a new BuiltinArgument
struct, which contains the old strictness boolean and also a static
`name` str - this is automatically determined via the ident for the
corresponding function argument in the proc-macro case, and passed in in
the cases where we're still manually calling Builtin::new.

Currently this name is unused, but in the future this can be used as
part of a documentation system for builtins.

Change-Id: Ib9dadb15b69bf8c9ea1983a4f4f197294a2394a6
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7204
Reviewed-by: tazjin <tazjin@tvl.su>
Tested-by: BuildkiteCI

tvix/eval/src/value/mod.rs

@@ -20,7 +20,7 @@ use crate::errors::ErrorKind;
 use crate::opcode::StackIdx;
 use crate::vm::VM;
 pub use attrs::NixAttrs;
-pub use builtin::Builtin;
+pub use builtin::{Builtin, BuiltinArgument};
 pub(crate) use function::Formals;
 pub use function::{Closure, Lambda};
 pub use list::NixList;