refactor: canonicalize moved paths that refer to item left behind

[ahomescu]

Follow-up limitation found while writing the test — FIXED: items moved out
of a header could not rely on bindings that stay behind in the header (e.g.
the kept glob). A bare path like thing that resolved through the glob was
not canonicalized on the way out (is_relative_path treats only
self::/super:: as relative), so the moved item failed to compile with
E0412. move_items now runs canonicalize_moved_decl_paths over every
moved declaration (and its impl block): a single-segment path to a local,
non-moving item def is rewritten to its absolute path via def_qpath.
Paths are left alone when the destination module still binds the ident to
the same def — through a pre-existing import, an import moving along with
the declaration (moved use targets are now recorded in
ModuleInfo::import_targets, mirroring update_module_info_items), or
because the target is defined in the destination module itself — which
keeps the existing snapshots byte-identical. Paths to moved defs are still
rewritten later by update_paths via path_mapping. The
reorganize_glob_import test now uses the bare thing field type and
verifies it becomes crate::defs::thing.

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[thedataking]

Review of stack 1953: qualifying a moved path drops its generic arguments.

[thedataking]

[P2] Preserve generic arguments when qualifying a path

def_qpath(def_id) reconstructs the definition's name without the original path's generic arguments. This turns a field type Value<i32> into crate::defs::Value, causing E0107. The destination's glob import makes this a regression: the output before this PR already compiled because Value<i32> remained resolvable there. Please carry the original segment's generic arguments onto the qualified path.

This case uses a generic Rust type; it applies to code that has already been edited after transpilation.

Reproducer

The input compiles. Run c2rust-refactor reorganize_definitions --rewrite-mode alongside -- repro.rs --edition=2021 and compile the resulting repro.new to see E0107.

#![feature(register_tool)]
#![register_tool(c2rust)]
#![allow(dead_code, non_camel_case_types, unused_imports)]

pub mod defs {
    pub struct Value<T> { pub val: T }
}
pub mod user {
    use crate::defs::*;
    #[c2rust::header_src = "/tmp/user.h:1"]
    pub mod user_h {
        use crate::defs::*;
        pub struct config { pub thing: Value<i32> }
    }
    pub fn go(_: user_h::config) {}
}
fn main() {}