Eliminate using clones for TokenMap methods and return references instead.

[JoshuaBatty]

We are doing a lot of clones when returning Idents and Tokens in the language server.

This is primarily to get around ownership issues associated with read/write locks inherit with DashMap.

We now have 2 seperate stages in the server, the first uses DashMap to populate the tokens during AST traversal. The second stage writes the result to a read only map. Currently this type (for example a HashMap) needs to be wrapped in an RwLock to allow for interior mutability because of tower-lsp. Once we remove our dependance on that crate we will be able to use a regular HashMap which should allow for us to return references pretty easily. Should lead to a nice performance win.

[JoshuaBatty]

This was implemented in #5509