Merge #6172

6172: Add qualify path assist r=matklad a=Veykril

This implements a `qualify_path` assist which works quite similar to the `auto_import` assist but instead of adding imports to the file it well, qualifies the path. This PR also moves out the `AutoImportAssets` struct and functions from `auto_import` into a utils submodule as most of this is now shared between `auto_import` and `qualify_path`.

Changes made to `AutoImportAssets` are solely in its `search_for_imports` function which now takes a prefixed parameter to discern between using `find_use_path_prefixed` and `find_use_path` as the former is the required behavior by `auto_import` and the latter by this assist.

For missing imported traits instead of importing this will qualify the path with a trait cast as in:
```rust
test_mod::TestStruct::TEST_CONST<|>
```
becomes
```rust
<test_mod::TestStruct as test_mod::TestTrait>::TEST_CONST
```

and for trait methods ideally it would do the following:
```rust
let test_struct = test_mod::TestStruct {};
test_struct.test_meth<|>od()
```
becomes
```rust
let test_struct = test_mod::TestStruct {};
test_mod::TestTrait::test_method(&test_struct)
```

Fixes #4124.

Co-authored-by: Lukas Wirth <lukastw97@gmail.com>

crates/syntax/src/ast/make.rs

@@ -172,6 +172,9 @@ pub fn expr_call(f: ast::Expr, arg_list: ast::ArgList) -> ast::Expr {
 pub fn expr_method_call(receiver: ast::Expr, method: &str, arg_list: ast::ArgList) -> ast::Expr {
     expr_from_text(&format!("{}.{}{}", receiver, method, arg_list))
 }
+pub fn expr_ref(expr: ast::Expr, exclusive: bool) -> ast::Expr {
+    expr_from_text(&if exclusive { format!("&mut {}", expr) } else { format!("&{}", expr) })
+}
 fn expr_from_text(text: &str) -> ast::Expr {
     ast_from_text(&format!("const C: () = {};", text))
 }