fix(es/lints): Fix const-assign in function expressions (#6294)

crates/swc/tests/errors/lints/const-assign/1/input.js

@@ -31,3 +31,8 @@ b &&= 10;
 c ||= 10;
 
 d ??= 10;
+
+const fn = () => {
+  const e = 100;
+  e = 200;
+};

crates/swc/tests/errors/lints/const-assign/1/output.swc-stderr

@@ -518,3 +518,13 @@
     : |
     : `-- cannot reassign
     `----
+
+  x cannot reassign to a variable declared with `const`
+    ,-[36:3]
+ 36 | const e = 100;
+    :       |
+    :       `-- const variable was declared here
+ 37 |   e = 200;
+    :   |
+    :   `-- cannot reassign
+    `----

crates/swc_ecma_lints/src/rules/const_assign.rs

@@ -108,11 +108,13 @@ impl Visit for ConstAssign {
         program.visit_children_with(self);
     }
 
-    fn visit_var_decl(&mut self, var_decl: &VarDecl) {
+    fn visit_var_declarator(&mut self, var_declarator: &VarDeclarator) {
         let old_is_pat_decl = self.is_pat_decl;
         self.is_pat_decl = true;
-        var_decl.visit_children_with(self);
+        var_declarator.name.visit_with(self);
         self.is_pat_decl = old_is_pat_decl;
+
+        var_declarator.init.visit_with(self);
     }
 }