Switch from Vec<InlayKind> to object with props

- Instead of a single object type, use several individual nested types
  to allow toggling from the settings GUI
- Remove unused struct definitions
- Install and test that the toggles work

crates/rust-analyzer/src/world.rs

@@ -33,7 +33,7 @@ pub struct Options {
     pub publish_decorations: bool,
     pub supports_location_link: bool,
     pub line_folding_only: bool,
-    pub inlay_hint_opts: InlayConfig,
+    pub inlay_hints: InlayConfig,
     pub rustfmt_args: Vec<String>,
     pub cargo_watch: CheckOptions,
 }