refactor: move convert module to stable_mir

note that this commit delete `convert/error.rs`, we would use `SmirError::from_internal` instead.

**Unresolved questions:**
- There are still a few direct calls to rustc's internals scattered across `impl Stable`s, but most of them appear to be relatively stable, e.g., `mir::interpret::ConstAllocation::inner(self)` and `mir::syntax::SwitchTargets::otherwise(self)`.

Author: makai410

compiler/rustc_smir/src/rustc_internal/mod.rs

@@ -17,13 +17,12 @@ use rustc_span::Span;
 use rustc_span::def_id::{CrateNum, DefId};
 use scoped_tls::scoped_thread_local;
 use stable_mir::Error;
+use stable_mir::convert::{RustcInternal, Stable};
 
 use crate::rustc_smir::context::SmirCtxt;
-use crate::rustc_smir::{Stable, Tables};
 use crate::rustc_smir::{Bridge, IndexedVal, SmirContainer, Tables};
 use crate::stable_mir;
 
-mod internal;
 pub mod pretty;
 
 /// Convert an internal Rust compiler item into its stable counterpart, if one exists.
@@ -340,11 +339,3 @@ impl<K: PartialEq + Hash + Eq, V: Copy + Debug + PartialEq + IndexedVal> Index<V
         k
     }
 }
-
-/// Trait used to translate a stable construct to its rustc counterpart.
-///
-/// This is basically a mirror of [crate::rustc_smir::Stable].
-pub trait RustcInternal {
-    type T<'tcx>;
-    fn internal<'tcx>(&self, tables: &mut Tables<'_>, tcx: TyCtxt<'tcx>) -> Self::T<'tcx>;
-}

compiler/rustc_smir/src/rustc_smir/convert/error.rs

@@ -22,7 +22,6 @@ use crate::rustc_internal::IndexMap;
 pub mod alloc;
 mod builder;
 pub mod context;
-mod convert;
 
 /// A container which is used for TLS.
 pub struct SmirContainer<'tcx, B: Bridge> {

compiler/rustc_smir/src/rustc_smir/mod.rs

@@ -8,6 +8,7 @@ use std::cell::Cell;
 use rustc_hir::def::DefKind;
 use rustc_smir::{Bridge, SmirContainer, Tables};
 use stable_mir::abi::{FnAbi, Layout, LayoutShape};
+use stable_mir::convert::{RustcInternal, Stable};
 use stable_mir::crate_def::Attribute;
 use stable_mir::mir::alloc::{AllocId, GlobalAlloc};
 use stable_mir::mir::mono::{Instance, InstanceDef, StaticDef};