refactor(tvix/eval): merge all bindings creation logic

As of this commit, all three types of bindings scopes are compiled the
same way (i.e. compilation of non-recursive attribute sets has been
switched over to the new code paths).

This sets us up for doing the final implementation of nested attribute
sets.

HOWEVER, this breaks the existing implementation of nested attributes
in non-recursive attribute sets. That implementation is flawed and
unworkable in practice, so we need to do this dance to be able to
implement it correctly.

Change-Id: Iba2545c0d1d6b51f5e1a31a5d005b8d01da546d3
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6782
Reviewed-by: sterni <sternenseemann@systemli.org>
Tested-by: BuildkiteCI

tvix/eval/src/compiler/mod.rs

@@ -20,7 +20,6 @@ mod spans;
 use codemap::Span;
 use path_clean::PathClean;
 use rnix::ast::{self, AstToken, HasEntry};
-use rowan::ast::AstChildren;
 use smol_str::SmolStr;
 use std::collections::HashMap;
 use std::path::{Path, PathBuf};