Improve inlay hinting for types

Add hints for types in for loop expressions.
Resolve types for every tuple parameter.
Refactor the code.

crates/ra_lsp_server/src/main_loop/handlers.rs

@@ -897,6 +897,9 @@ pub fn handle_inlay_hints(
             kind: match api_type.kind {
                 ra_ide_api::InlayKind::LetBindingType => InlayKind::LetBindingType,
                 ra_ide_api::InlayKind::ClosureParameterType => InlayKind::ClosureParameterType,
+                ra_ide_api::InlayKind::ForExpressionBindingType => {
+                    InlayKind::ForExpressionBindingType
+                }
             },
         })
         .collect())

crates/ra_lsp_server/src/req.rs

@@ -215,6 +215,7 @@ pub struct InlayHintsParams {
 pub enum InlayKind {
     LetBindingType,
     ClosureParameterType,
+    ForExpressionBindingType,
 }
 
 #[derive(Debug, Deserialize, Serialize)]