helix-lsp-types: use bitflags::bitflags rather than extern crate

This seems to be a historical artifact in `lsp_types` - we can use a
regular `use` statement to pull in the `bitflags!` macro rather than
an external crate definition. This fixes rust-analyzer's ability to find
the macro at least on rust-analyzer 2024-02-26.

helix-lsp-types/src/lib.rs

@@ -16,8 +16,8 @@ able to parse any URI, such as `urn:isbn:0451450523`.
 */
 #![allow(non_upper_case_globals)]
 #![forbid(unsafe_code)]
-#[macro_use]
-extern crate bitflags;
+
+use bitflags::bitflags;
 
 use std::{collections::HashMap, fmt::Debug};