Allow the if_not_else Clippy lint

Specifically, the [`if_not_else`] lint will sometimes flag
code to change the order of `if` and `else` bodies if this
would allow a `!` to be removed. While perhaps tasteful in
some cases, there are many cases in my experience where this
bows to other competing concerns that impact readability.
(Such as the relative sizes of the `if` and `else` bodies,
or perhaps an ordering that just makes the code flow in a
more natural way.)

[`if_not_else`]: https://rust-lang.github.io/rust-clippy/master/index.html#/if_not_else

crates/ty_server/src/session.rs

@@ -790,7 +790,6 @@ impl Session {
         // But while this seemed to work for the project root, it
         // simply wouldn't result in any file notifications for changes
         // to files outside of the project root.
-        #[allow(clippy::if_not_else)] // no! it reads better this way ---AG
         let watchers = if !self.client_capabilities().supports_relative_file_watcher() {
             tracing::warn!(
                 "Your LSP client doesn't support file watching outside of project: \