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/req.rs

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