Auto merge of rust-lang#14948 - alibektas:14386, r=Veykril

feature : assist delegate impl

This PR ( fixes rust-lang#14386 ) introduces a new IDE assist that generates a trait impl for a struct that delegates a field. This is a draft because the current `ide_db::path_transform::PathTransform` produces some unwanted results when it deals with extern crates, an example of which I attach as a GIF.

GIFs :
1. A general case
![14386-functional](https://github.com/rust-lang/rust-analyzer/assets/20956650/22114959-caa6-45ec-a154-b4b2f458f6b1)

2. A case where `ide_db::path_transform::PathTransform` fails to correctly resolve a property ( take `Allocator` as an example ) to its full path, thus causing an error to occur. ( Not to even mention that resolving this causes another error `use of unstable library feature 'allocator_api'` to occur
![14386-erroneous](https://github.com/rust-lang/rust-analyzer/assets/20956650/922ca715-594e-4168-a579-7c5c006f93aa)

Author: bors