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/lib.rs

@@ -37,7 +37,7 @@ pub use crate::vm::run_lambda;
 /// Internal-only parts of `tvix-eval`, exported for use in macros, but not part of the public
 /// interface of the crate.
 pub mod internal {
-    pub use crate::value::Builtin;
+    pub use crate::value::{Builtin, BuiltinArgument};
     pub use crate::vm::VM;
 }