Add static semantic token modifier for associated functions with no &self

refactor logic into code_model.rs

address comments

Author: Anatol Liu

crates/hir/src/code_model.rs

@@ -789,11 +789,7 @@ impl Function {
     }
 
     /// whether this function is associated with some trait/impl
-    pub fn is_associated(self, db: &dyn HirDatabase) -> bool {
-        if self.self_param(db).is_some() {
-            return false;
-        }
-
+    pub fn is_assoc_item(self, db: &dyn HirDatabase) -> bool {
         let fn_parent_kind = self
             .source(db)
             .value

crates/ide/src/syntax_highlighting.rs

@@ -746,7 +746,7 @@ fn highlight_def(db: &RootDatabase, def: Definition) -> Highlight {
                 if func.is_unsafe(db) {
                     h |= HighlightModifier::Unsafe;
                 }
-                if func.is_associated(db) {
+                if func.is_assoc_item(db) && func.self_param(db).is_none() {
                     h |= HighlightModifier::Static;
                 }
                 return h;